- “You wear a helmet in the gym shower one time and you're labeled for life!”
- ―Marco's rant about his safe kid monitor
Marco Diaz is the deuteragonist of the Disney XD animated series, Star vs. the Forces of Evil. A Latino-American California citizen, he has been assigned the task of helping Star Butterfly adjust to life on Earth. He has also come to serve the additional roles of aiding Star in fighting all matter of inter-dimensional monsters and apparently has even begun to form a friendship of sorts with her. By the series finale, he becomes Star's boyfriend.
Marco is practically the exact opposite of Star. He is very wary and tries to avoid any trouble or exposure. Because of Marco's cautiousness (and the one time he wore a helmet in the gym shower), he is labeled by both his peers and school staff as the "safe kid". Ironically, despite his predilection toward practical caution, Marco seems to enjoy the prospect of combat and adventure (In the pilot episode, he even expressed a desire for "some action and danger in (his) life"). Marco also seems to want this to be opined so with his reputation, as well; Marco openly expresses disdain for being considered a "Safe Kid", and has repeatedly attempted (to little avail) to persuade others to view him as otherwise.
Marco has proven to be notably irritable, as seen in his rambling about his reputation in the pilot episode, and his very quickly losing patience with Star in the same episode. He has also demonstrated poor sportsmanship, elevating himself and slandering his opponents in the Arcade Dimension of the episode immediately following, though this may have simply been on account of his anger and defensiveness against Pony Head, due to her mistreatment and threats against him.
Marco seems to have studied martial arts extensively, namely Karate, as seen in the pilot episode, in which he employs it to combat the monsters who come to assassinate Star (even explaining it as such to her). He can also briefly be seen in the introductory animated sequence about to break a wooden board, a common test of strength and technique in East-Asian martial arts.
Marco is a medium-sized kid with a slender build, tan skin, dark brown hair, and brown eyes. He also has a small mole on his right cheek. He is typically shown wearing a light gray shirt, a red hoodie jacket, dark gray jeans, and an olive-and-white pair of sneakers. In episodes like "Sleepover", he wears a turquoise vest instead of his red jacket.
In "Running with Scissors", Marco is shown as a thirty-year-old, and is more muscular and has a five-a-clock shadow. He still wore his typical red hoodie, but it has been worn and torn with age. He also wore a brown unzipped biker jacket with rolled-up sleeves, gray torn-up pants, a rope belt, black boots, and black fingerless gloves. He also had a black slash painted across his left eye, two piercings on his right ear, and a tattoo of dimensional scissors on his inner left bicep. Eventually, though, Marco returns to his original appearance at the end of the episode.
- Karate: Marco is learning and currently has a red belt in karate. He is very capable of using karate chops, kicks, and punches to battle monsters at the same level as Star.
- Culinary prowess: Marco is good at making nachos. In "Pizza Thing", he makes a pizza with Pony Head, which doesn't turn out especially good.
- Academics: In "Match Maker", it is shown that Marco has good math skills, getting good grades (including an A in psychology) and in "Quest Buy", using the metric system to find a charger for Star's wand at Quest Buy. However, he admits in "Naysaya" that he doesn't know how to do long division.
- Swordsmanship: As of "Running with Scissors", Marco has become proficient at wielding a one-handed sword.
- Survival skills: Sixteen years of experience hunting Hekapoo has turned Marco into a hardened survivor and warrior. Upon returning to his original age on Earth, it is unknown if he has kept these skills.
Role in the series
In the Pilot episode, Marco was chosen by his school's principal to guide and show Star around the school due to his reputation. As he discovered upon returning home on the same day (after having discovered Star's bizarre background at the end of the tour he had given her), his home had also been selected to be Star's own, though the person or persons who made this decision and the means by which it was reached remain unknown.
Immediately following his interactions with Star, Marco ran away from home, abhorrent of his new roommate. Star managed to find him afterwards and acknowledged the hardship she had put him through. Prior to the closure being fully reached, the two were ambushed by the villain Ludo and his thugs. After having helped to ward off the assassination attempt, Marco expressed a change of heart toward Star and a preference for her to remain a resident of his home. The two-headed back to Marco's house following this reconciliation.
Marco spends much of the season acting as a straight man to Star's foil. He gets caught in a variety of situations such as getting a monster arm and growing a beard. He also unknowingly becomes connected to Star after they dance underneath the Blood Moon. At the end of the first season, Marco is kidnapped by Toffee but is rescued by Star, only to witness her wand getting damaged.
Marco starts to try to expand his ability to help Star such as getting a red belt and wondering about his future. He also slowly but surely becomes friends with Tom Lucitor, Star's ex-boyfriend who had initially tried to kill him when he thought they were together. He also begins to openly pursue Jackie-Lynn Thomas whom he has had a crush on since he was in kindergarten. They finally begin dating in "Bon Bon the Birthday Clown", but he becomes oblivious to Star's feelings towards him. He befriends Kelly, a girl with large turquoise hair, and Hekapoo, a member of the Magic High Commission who bequeaths a pair of dimensional scissors to him after he chased her in the Neverzone for several years.
Marco also gains the ire of Miss Heinous after getting her kicked out as the dean of St. Olga's Reform School for Wayward Princesses, though he views her more as a nuisance than an actual threat. Marco eventually discovers that Star does indeed have a crush on him, but after accepting her denial of it, becomes broken when she is forced to leave earth and head back to Mewni to face Toffee, leaving him dejected.
Marco follows Star to Mewni and aids her in defeating Toffee and restoring order. He returns to earth afterwards, but will not stop talking about his adventures to his friends. Jackie-Lynn politely breaks up with him and, in a reversal of the series beginning, decides to go to Mewni as an exchange student. His meeting with Star ends up being awkward, especially when she reveals that she is dating Tom again, but soon the two of them resume their friendship and begin going on more adventures with Star dubbing Marco a squire.
Marco begins to partake in side missions so that he can be promoted to a knight and even reveals his identity as Princess Turdina who had viewed him as an idol for princesses. Eventually, he begins to feel miserable when he realizes that he may have feelings for Star, but cheers up when he stays in Kelly's presence; starting a slight relationship with her.
When Miss Heinous discovers that she is Meteora, the long lost daughter of Eclipsa, she goes on a rampage to destroy Mewni. Marco uses himself as bait to defeat her, but has his soul sucked out. Eventually, Star and Eclipsa defeat Meteora by turning her back into a baby and Marco's soul is restored.
Marco begins the first half of the season continuing to help Star with finding her mother Moon, who had disappeared. After finding her, Marco decides to pursue a relationship with Kelly, whom he refers to as a "break up buddy", though they later break up off-screen. He and Star decide to be rid of the Blood Moon curse which Tom obliges by using a Severing Stone. Convinced that it worked, Marco continues to the rest of the half becoming a knight before returning to earth with Janna. Star decides to stay with him and his family (who have welcomed a baby girl named Mariposa) after she realizes that she does not know what to do with herself.
When all teleportation facets to Mewni cease to work, Marco, Star, Tom and Janna decide to look for a well that can transport them there. Tom, who had recently broken up with Star, tells Marco that he should be with her regardless of the curse. Upon arriving in Mewni, they learn that Mina Loveberry has started an uprising and take part in the final battle. Marco and Star finally admit that they still have feelings for each other and begin a serious relationship.
Star decides to destroy magic completely by heading straight into the magic realm and performing the whispering spell. This succeeds, but Star learns that she and Marco cannot be together as once the spell is performed, everyone goes back to their respective dimensions. Marco and Star embrace each other as the magic realm closes for good. However, their magic proves to be so strong, that earth and Mewni fuse together and the series ends with Marco and Star reunited for good.
- Originally, in Daron Nefcy's version of Star without magical powers, Marco was named Sol, had an obsession with Dragon Ball Z (where his karate interest came from), and was more like an enemy to Star.
- In the midst of production, Marco was originally to have braces.
- In the unaired pilot, Marco's pants were originally blue instead of dark gray.
- Marco's middle name was revealed to be Ubaldo in "Match Maker".
- Marco's initials spell "MUD". This is purely coincidental, of course.
- The names "Marco" and "Ubaldo" are of Italian origin.
- Marco, during Season One, had a green belt with a white stripe in the Tang Soo Do discipline. A green belt represents "the growth of a seed that sprouts upward, becoming a plant. Like the sprout, the student is becoming something greater." A green belt is roughly middle level.
- Marco's fans are called "Meatballs" by Adam on his Twitter.
- Marco and Miguel Rivera from Coco bear a close resemblance to one another. As a matter of fact, Miguel was originally going to be named Marco, but had his name changed when one of the animators found out that he looked like Marco.
- Marco getting his GED was based on Daron Nefcy's personal experience. She had been bullied in high school and decided to drop out and get a GED instead.
- "Reddit Post". Reddit (August 3, 2019).