Rex may look like the most fearsome dinosaur in the toy box, but this tyrannosaurus is one of the most lovable toys of the bunch. Despite his endless worries and insecurities about his small roar, Rex always comes through for his pals.
Rex was created as the token dinosaur for Andy's toy collection and has a similar build to the Tyrannosaurus from the Dino-Riders toy-line. Joss Whedon is credited with the creation of the Rex character. In the original story pitch for Toy Story, Rex's personality was mostly the same as in the final film (although his reaction to the birthday was even more horror-struck and devastated, where he clung to Slinky while sobbing and yelling that they're "doomed" mid-sobs), except that he also showed himself to get very angry and vengeful when Woody callously admits to throwing Buzz out of the window on purpose.
Despite his portrayal as a ferocious Tyrannosaurus Rex, Rex is ironically gentle, kind, and caring, and he hates any kind of argument or confrontation. Though his vocabulary is fairly strong, he is somewhat absent-minded and tends to cause accidental mayhem due to his size and obliviousness.
Rex also suffers from anxiety. He fears being replaced or abandoned, either at the prospect of being thrown away or the arrival of a newer, more ferocious dinosaur toy. Despite his fears, he finds happiness and enjoyment in most things; one of his favorite pastimes include playing video games with his friends, a hobby in which Rex has shown a fair amount of talent. With his childlike demeanor and lack of self-confidence, Rex is the most innocent of all the toys and shows the greatest desire to be loved and played with. Largely because of his innocence, he also can show himself to be very gullible, which is especially evident in the Small Fry short, where he was the only one of the toys to believe that Buzz Lightyear had "shrunk" from contact with the balls in the ball pit when the rest of the toys quickly realized the "Buzz" that was brought home was an impostor due to his obvious short stature. Despite his constant fear of rejection, he is a valued member of the gang and considered to be the most "ferocious" dinosaur toy a kid could ask for in the eyes of both Andy and Bonnie.
In the original film, Rex is first seen when Woody is planning for a staff meeting. He finds his doodle pad by Molly's crib and asks out loud who put it there. Suddenly, Rex appears and roars in Woody's face, but Woody nonchalantly asks him how he's doing in the middle of it. As Rex stops his roar, he asks Woody if we were scared and to be honest. Woody tells him he was close to being scared that time, to which a disappointed Rex says that he was going for fearsome, but he doesn't feel it, and (ironically) says that he feels like he's coming off as annoying. Later, as the staff meeting begins, Woody first asks if everybody has a moving buddy for when Andy's family moves next week, to which Rex says that he didn't know they were supposed to have one already. As Woody emphasizes that every toy must have a moving buddy and other minor news, Woody then attempts to briefly mention that Andy's birthday party has been moved to today. But the toys obviously freak out, with Rex confused that it's moved today since Andy's actual birthday is until next week. Woody then tells them that they all go through the same thing every birthday and Christmas, but Rex is scared that Andy will get a better (and meaner) dinosaur and says that he couldn't take that kind of rejection. But Woody calms him and the others down by saying that it doesn't matter how much they're played with, but their job is to be there for Andy when he needs them. Suddenly, Hamm interrupts him by yelling that Andy's birthday guests are arriving, causing Rex to scream and the toys to climb the bookshelf and charge towards the window. As they look out the window, Hamm says the toys are next month's yard sale flooder. Rex then asks him if they are any dinosaur-shaped ones, but Hamm calls him an idiot and stating that all the gifts are obviously in boxes. Rex gets nervous as the presents keep getting bigger. Slinky tries to calm him and the other toys down by saying he sees a kid carrying a smaller present, but as he turns around, the present turns out to be a long one, causing the toys to screaming in terror as they shake the blinds. Woody yells at them and asks if he sent out the troops to spy on Andy's party, would they all calm down. Rex speaks for all of them and yells that they promise, to which Woody yells at him and the others to "save their batteries." He and the others watch as Sarge and his troops march out to the hallway with Molly's baby monitor to communicate with the toys. The toys then gather around Andy's nightstand as Woody sets up the monitor. Later, Sarge comes on to monitor as Andy begins to open his presents. Rex is frozen with anticipation until Mr. Potato Head begins to chant for one of the presents to contain a Mrs. Potato Head doll, much to the confusion of the others. After Andy has opened up all his presents (which all turned out to be non-toy items), the toys celebrate in victory. But as the Green Army Men are about to pack up, they stop when Mrs. Davis whips out a surprise present from the closet. As he tells the fearful toys through the monitor what it is, the monitor begins to static. Rex begins to shake the nightstand in frustration as the monitor falls to the ground and the batteries pop out. Hamm and Mr. Potato Head berate him for this as they struggle to put the batteries incorrectly. A frustrated Woody then shoves them out of the way and puts the batteries in their correct place when Sarge suddenly tells them that Andy and his friends are coming upstairs with the new toy, causing them all to sprint back to their positions. Rex is running and panicking when he crashes into Andy's garbage can and tips over frozen.
On the day of Andy's birthday, Rex fears that Andy will get a newer, better dinosaur toy and replace him, though this is not the case as Andy instead receives a Buzz Lightyear figure, to whom Rex immediately takes a shine to like the other toys. Throughout the following days, Rex and Buzz form a friendship. Buzz, at one point, helps Rex master his roar, which he uses to blow the pieces off of Mr. Potato Head.
When Woody's jealousy gets the better of him, causing Buzz to fall out the window, Rex is reluctant on whether or not to place the blame on Woody as he does not like confrontations. When Woody is thrown out of the group for his apparent selfishness, Rex is remorseful but overall in agreement with the rest of the toys. His tune changes, however, when both Woody and Buzz appear to be working together to reunite with Andy, leaving Rex feeling guilty with the other toys.
At the end of the film, Christmas has arrived and the toys anxiously await to see what new toys Andy has gotten. Rex, who has garnered some confidence over the course of the film, openly hopes that Andy gets a leaf-eater dinosaur, so that he may play the dominant predator.
In Toy Story 2, Rex has since become a fan of the Buzz Lightyear: Attack on Zurg video game. Unfortunately, he is unable to beat the game, mostly due to his small arms preventing him from pressing certain buttons at the same time, resulting in numerous disappointments.
Later on, at a yard sale, Woody is stolen by Al McWhiggin, the owner of Al's Toy Barn. As the toys try to analyze the crime, Rex tries to write a message to the FBI for help, but he didn't knew how to write FBI, so he asked if somebody knew how to do it, accidentally destroying the crime scene recreation that Mr. Potato Head built, and is with the rest of the toys when Buzz realizes who kidnapped Woody. He is then seen channel-hopping in an attempt to find Al's Toy Barn commercial, but Hamm eventually takes over, doing it far more rapidly because he was annoyed with how Rex channel-hopped. Buzz establishes a rescue mission, with Rex—who believes his experience with video games have prepared him for the adventure—as one of the recruited toys. At Al's Toy Barn, Rex reads a "Buzz Lightyear" video game strategy guide and finally discovers how to defeat Zurg. He later attracts Buzz #2 (unaware he was not Andy's Buzz) with his claim of knowing how to defeat Zurg.
In Al's office, Rex tells Buzz #2 about a secret entrance from the game (the shadows to the left, which Buzz uses to find the vents later). His tail sticking out of Al's bag also lets the real Buzz know where the others are.
The toys later travel to Al's apartment, where Buzz #2 and the toys use literally Rex's head as a battering ram (with Rex protesting Buzz's order to "use [Rex's] head") to break in. Unfortunately, they learn that Woody wants to stay with Al and his "Roundup gang", as a means of self-preservation. Woody's mind eventually changes, however, but he is stopped by Stinky Pete and taken by Al before he can be reunited with Rex and the others. Rex, Buzz, and the other toys try to follow Al using the elevator, but they are confronted by Zurg in pursuit of Buzz, much to Rex and Buzz #2's shock. A battle ensues between Zurg and Buzz #2. When Zurg eventually gaining the upper hand, Rex tried to warn the others of the peril, before telling Buzz #2 that he could have defeated Zurg all along if he believes in himself. As Zurg prepares to finish Buzz #2 off, Rex couldn't bear to look and turns around in fear, inadvertently knocking Zurg off the elevator shaft and accomplishing his goal of defeating the evil emperor.
At the end of the film when Hamm is playing the video game, he asks Rex for help, but Rex proudly replies, "I don't need to play; I've lived it!"
One of the bloopers shows the scene where the toys use him as a battering ram, only for them to crash and Rex to hurt his head when banged against the locked grate which did not even budge making him say "Ow!".
Rex has a cameo in the outtakes of the film. In the film, as Sulley and Mike walk towards the crosswalk, they stand next to a large, green monster named Ted. Sulley yells good morning to him, to which he clucks in response. In the outtakes, Sulley still greets him in the same fashion, but it is now a large Rex who roars instead of clucking. The director offscreen yells cut and Rex asks how was his acting. The director thanks him for his time, but Rex insists he could do better and be taller, only for the director to ask for the next auditioner. He does not seem to have his tail in the outtakes.
Rex cameos as an inanimate object in WALL-E's collection. As the robot arrives home from his day at work, he opens his door to show his large collection of objects, including a Rex dinosaur toy (located between a pair of bowling pins).
Rex returns in the third film, as he eagerly awaits the opportunity to finally get played with by children again. Years later, Andy is 17 years old, and Rex, like the other toys, wishes so much to be played with that he even gets excited when Andy picks him up. The toys are accidentally almost thrown away by Andy's mom, thinking that they are trash. Rex was responsible for saving the toys' lives with his pointy tail to split open the trash bag. With them believing that they are just junk to Andy now, they decide to sneak into a box bound for Sunnyside Daycare.
Once at Sunnyside, they are welcomed by the other toys that reside there, led by Lotso, the strawberry-scented bear (as remarked by Rex), who show that Sunnyside is a paradise for toys where you will be played with by generations and generations of kids. The toys there take Rex and the others to the Caterpillar Room, telling them that they will soon be played with by children. When the kids are returning to the room, Rex eagerly waits in front of the door, excited that he is finally going to get some playtime. However, when the kids enter, it is discovered that they are very little children who have no regard for treating a toy right, even breaking off Rex's tail. When the toys try to complain to Lotso, it is revealed that they were sent to the Caterpillar Room to be beaten up by the toddlers on purpose and that you have to earn joining the Butterfly Room. Lotso even reprograms Buzz so that he is back to being a senseless astronaut who keeps Rex and the toys in shelved baskets (which function as prison cells).
The next day, following another rough playtime with the toddlers, Woody returns to Sunnyside, and Rex and the other toys are elated to see him again. Woody then formulates an elaborate plan to help the toys escape Sunnyside and make it back to Andy. That night, Rex and Hamm distract Buzz by staging a little fight, and when Buzz attempts to break off the fight, Jessie calls to him and entraps Buzz in a plastic storage bin, then Rex and Hamm immediately jump onto the bin prevent his escape. However, Buzz breaks himself free, and Rex and Hamm tackle him down from the side to prevent him from escaping. In order to reset Buzz, Woody has Rex insert his finger into a tiny hole below the switch, which causes Buzz to shut down for a brief second, then spring back to life in his Spanish deluded version. After a series of attempts and planning, the toys finally escape Sunnyside through the trash chute but are confronted by Lotso, who had "broken" Chatter into informing him of the escape plan, along with several of his henchmen. Woody, having been informed of Lotso's past, brings up the subject of Daisy, making Big Baby (and by extent the other Sunnyside toys) turn on Lotso.
After Big Baby throws Lotso in the chute, one of the alien's feet gets stuck in the lid. Woody goes in to help, but Lotso grabs him and puts him inside the trash chute. Rex and the toys follow to save him. But then they are picked up by a garbage truck and taken to the dump. Rex was the last one to get a metal object and hung onto a fan that clung to a metal conveyor belt. When approaching the incinerator a few feet away from where they were, Rex mistakes it for daylight. Woody points out that it is not daylight, it turns out to be fire. Rex held Hamm and Potato Head's hand when they thought they were about to die. But they got rescued by the Aliens.
When the toys make their way back home, they clean themselves of the dirt and grime that had made its way onto them during their escape. The toys aside Woody climb into a box bound for the attic and they say goodbye to him; Rex tells Woody to take care of Andy. However, Woody decides that the toys deserve a better place than the attic so he writes to Andy to donate the toys to Bonnie Anderson. Andy arrives at Bonnie's house and gives his toys to her; when he shows Rex to Bonnie, he makes roaring sounds as if Rex is roaring, making her recoil initially, but she chuckles as she notices that it's just a toy and takes Rex.
After Andy leaves, Rex is briefly seen talking to Trixie, becoming close friends with her, as further shown in the film credits when the two dinosaur toys are seen playing a game on a computer together. Their cooperation pays off as they help each other reach the end of the game, then Trixie reaches her paws out to catch Rex's tiny arms in a high-five. Finally, Rex and Trixie are seen side by side as the toys enjoy watching Buzz and Jessie perform a pasodoble to "Hay Un Amigo En Mi" (the Spanish version of "You've Got a Friend in Me").
Rex appeared in all the Toy Story Toons shorts, with the most prominent appearance being "Partysaurus Rex" in which he served as the protagonist. He also played a minor role in "Small Fry", where he and Buzz are taken to Poultry Palace.
In the aforementioned "Partysaurus Rex", Rex accidentally spoils the fun of Mr. Potato Head and the other toys, who chastises Rex for his clumsiness. This triggers Rex's neurosis, but he is soon taken by Bonnie for playtime in the bathtub, where he befriends Bonnie's bath toys who want nothing more than to fill the tub and have an everlasting rave party. Unlike the other bath toys, Rex has arms and fingers, allowing him to refill the tub after Bonnie leaves. He receives instant praise from the bath toys and adopts the nickname "Partysaurus Rex". Unfortunately, the tub overflows and despite Rex's efforts to stop it, the house is soon flooded. Later on, Rex tries to tell his friends about his bath adventure, but none believe him until the pool toys call out to Rex to help them start a party of their own.
Rex is one of the two protagonists of the Christmas special and is first seen when Bonnie takes him, Trixie, and other toys to Mason's house. He is later seen walking among the Battle-saurs playsets with the others. To his delight, he is fitted with Battle-saur robot arms under the command of the Cleric and starts using them to do things he could no do with his usual stubby arms. Later, he is commanded against his will by the Cleric to use his arms to drop Buzz and Woody into a fan, which would incinerate them. Before being shredded, however, Bonnie and Mason enter the room, thereby stopping the Cleric's plan. The robot arms are later removed from Rex before he returns home with Bonnie.
Rex appears in the episode, "What is Time?" As Forky walks along with Old Timer (a toy clock that’s one of Bonnie’s baby toys), he asks the audience what is time. To help him, he introduces a toy who knows a lot about that: Rex (leaving Old Timer in the dust). The spork begins booing the dinosaur. When Rex asks why is he doing so, Forky simply says he doesn’t know, then proceeds to ask Rex the main question about time. Rex explains that “Now is now, stuff happens, then it’s later.”, much to the spork’s delight. Rex further explains that time can be the future or past. He uses dinosaurs roaming the Earth in the past as an example and says his kind, the tyrannosaurus rex, was known as the King of the Dinosaurs. He wishes he could have seen it. Forky asks what did the T-Rex eat, and Rex says they ate creatures from the Cretaceous period, such as Sauropods and Triceratops. Forky, at first, is impressed, but soon repeats the same question on what they ate. A confused Rex is about to repeat it but is soon interrupted when Forky asks if they ate with sporks. Rex explains that sporks weren’t invented since it was 65 million years ago, shocking Forky. Rex further explains that real dinosaurs ate with dagger-like teeth, before sadly saying the asteroid made them extinct shortly after. Forky is confused and believes he said, “Your hemorrhoid was a stink”. The dinosaur corrects him and says it was an asteroid, elaborating that it’s a giant ball that bounces on the Earth and wreaks havoc. Forky then grabs a small Pixar Ball and repeatedly smacks Rex with it on the nose, playfully impersonating an asteroid bouncing on the Earth. Rex tries to explain the actual impact on the asteroid collision, but Forky is too busy laughing as he continues smacking him with the ball, saying asteroids are fun. He then accidentally knocks Rex to the floor, but Rex sighs in defeat, saying that the asteroid always wins and the whole thing is depressing. Forky slowly scoots up next to him on the floor and says that while it may be inappropriate, he still repeats his question on what is time. Rex says time is a way to be forgotten since all the real dinosaurs are gone (with the exception of the millions of birds around the planet). Forky thinks for a minute and stands up. He tells Rex that while the future and the past sound great, he thinks he likes the now since he gets to spend time with him. Rex tells him that’s so nice and thank him. This causes the dinosaur to stand up with his confidence back and tells Forky that there are other toy dinosaurs in Bonnie’s room right now and whispers that he saw a “particularly tasty-looking sauropod” on the other side of the room. Forky says that sounds awful, but he tells him that he has a spork if he needs one, to which Rex says he thinks he does. He picks up the spork and roars that he is the terrible King of the Dinosaurs, with Forky yelling, “Here comes the hemorrhoid!” After the end-credits, the pair are then seen roaring and chasing after a confused wooden Sauropod toy on wheels.
Rex is one of the characters featured in the Toy Story world "Toy Box". When Sora, Donald, and Goofy arrive in Andy's Room, Rex mistakes him as Yozora, a character from the Verum Rex (an in-universe equivalent to Final Fantasy) video-game that he's playing, mentioning that he's had trouble beating a boss fight with the dragon Bahamut even after level-grinding.
Rex appears in the game as one of the unlockable and playable heroes with eighty tokens, he is a tank hero and is one of the characters who has to do more damage to enemies with a shield, also in his victory pose he becomes Partysaurus Rex.
In Toy Story on Ice, Rex has a wife named Mrs. Rex.
Rex is shown to be left-handed, as seen in Toy Story, where he shakes Buzz's left hand while meeting him for the first time.
Rex quotes a few of George McFly's lines from Back to the Future: "I don't like confrontations!" and "I don't think I could take that kind of rejection!"
In the first film, Rex states that he was made by a subsidiary of Mattel (coincidentally, real-life Rex toys are now made by Mattel and Thinkway).
At Toy Story Land at Disney's Hollywood Studios, an over-sized box for Rex is a queue element for Slinky Dog Dash, which lists his manufacturer as "Borealis", an homage to the model kit company "Aurora". The box's colorful artwork is reminiscent of many of their monster and dinosaur model kits.
In early concepts, Rex's character was originally an Apatosaurus.
In Toy Story 2, while inside Al's Toy Barn, Rex appears in a rear-view side mirror (viewed by Mr. Potato Head) as he tries to catch up with the car, parodying a scene from Jurassic Park where the Tyrannosaurus appears in a rear-view mirror when chasing a crew in a jeep (although for entirely different reasons as the T. Rex in the film was trying to eat the crew in the car, while Rex was attempting to get back in the car).
In Toy Story 3, when Rex appears out of the ground, the roar used for him was the Jurassic Park T. Rex roar.
Rex, despite being a toy Tyrannosaurus Rex, actually has three fingers on each hand instead of two in real life. However, this may have been intentional since Rex is a toy dinosaur, which, unless it was sold at a science museum gift shop or made for educational purposes, is actually not meant to be accurate.