- 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 Dinoriders toyline. 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 being portrayed as a ferocious Tyrannosaurus Rex, Rex is, ironically, gentle, kind, caring, and 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 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 imposter 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 making a failed attempt to scare Woody. He then reveals himself to be insecure about his roar, fearing that he is merely coming off as annoying rather than scary. At the time, Andy and his family are preparing to move to a new home, so the toys prepare by picking a moving partner to stick with during the transition. Rex is paired with Mr. Potato Head, much to the latter's annoyance.
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 to place the blame on Woody as he does not like confrontation. 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.
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 garage sale, Woody is stolen by Al McWhiggin of Al's Toy Barn. 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. Buzz establishes a rescue mission, with Rex—who believes his experience with video games have prepared him for the adventure— being one of the recruited toys. At Al's toy store, 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 (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 Rex's head as a battering ram 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 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. As a battle ensues, a fearful Rex cannot 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.
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 play time. 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 which 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. There, 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 bath overflows and deposits 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 main protagonists of the 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 play sets 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 makes a cameo during the credits of Monsters, Inc. auditioning for the role of Ted, a giant chicken, but Rex is soon dismissed despite him pleading for another take.
Rex is one of the characters featured in the Toy Story world "Toy Box". When Sora arrives in Andy's Room, Rex mistakes him as Yozora, a character from the Verum Rex (an in-universe equivalent to Final Fantasy) videogame that he's playing, mentioning that he's had trouble beating a boss fight with the dragon Bahamut even after level-grinding.
Rex does not exist as a walkaround character in the Disney theme parks but can be seen in a number of Toy Story related attractions.
A of Rex will appear as part of Slinky Dog Dash at Disney's Hollywood Studios perched on top of a Jenga block tower. In the same park, Rex has appeared in the Pixar Play Parade and stars in a mini-game alongside Trixie in Toy Story Mania.
Aside from the actual parks, Rex plays a major role in the musical stage adaption of the film on board the Disney Cruise Line. It was one of the few appearances of Rex as a walkaround character.
- 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!"
- His cameo in the Monsters, Inc. blooper reel is the first appearance Rex has made outside his franchise.
- According to the official movie magazine for Toy Story 3, Andrew Stanton is credited for the final design of Rex's face in the original film.
- 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).
- In early concepts, Rex's character was originally an Apatosaurus.
- In two of the Toy Story movies, Rex parodies Jurassic Park..
- In Toy Story 2, while inside Al's Toy Barn, Rex appears in a rearview side mirror (viewed by Mr. Potato Head) as he tries to catch up with the car, parodying a scene from Jurassic Park where a T-Rex 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, he roared with 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.
- As of 2013, Rex and Buzz are the only Toy Story characters to appear in every medium in the franchise.