He is portrayed by Xolo Maridueña.
Miguel and his family moved into the apartment complex where Johnny lived at. Miguel attempted to introduce himself to Johnny, but Johnny rebuffed him.
Later, while visiting the mini mart to pick up some Pepto Bismal for his grandma, Miguel accidentally outed Kyler and his cronies as not being college kids when they went to go buy beer. Miguel attempted to apologize, but Kyler and his crew began shoving him around, taking his Pepto Bismal and pouring it on his head as well as nicknaming him "Rhea" (short for diarrhea). However, after Miguel was shoved onto Johnny's car, Johnny stepped in and beat up Kyler and his gang.
Inspired by Johnny's karate moves, Miguel encouraged Johnny to open up his own karate dojo and teach him karate. Though Johnny initially shot down the idea, he later changed his mind and opened up his Cobra Kai dojo in the mini-mall, inviting Miguel to be his first student. The dojo would later receive a second student when Aisha Robinson joined.
When Kyler began harassing Sam LaRusso and lying by saying she performed oral sex on him, Miguel stepped in and told him to back off. Kyler responded by challenging him to a fight, at which point Miguel used his karate training to beat down Kyler and his three cronies, impressing Sam and the whole lunchroom. The fight was filmed and uploaded to YouTube where it went viral, resulting in tons of publicity for Cobra Kai.
Miguel eventually began dating Sam, though their relationship became strained by Sam's father Daniel LaRusso's dislike of Cobra Kai. Later, after getting drunk at a Cobra Kai party in a canyon, Miguel got into a misunderstanding with Sam where he assumed Robby Keene was her boyfriend and accidentally hit her while trying to attack Robby, resulting in their relationship breaking up.
Miguel and Cobra Kai later entered into the All Valley Under 18 Karate Tournament which Robby also entered into as an independent fighter. Miguel and Robby would face off in the final round, though by exploiting an injury Hawk had inflicted on Robby out of turn, Miguel was able to beat Robby and win the tournament for Cobra Kai. As the announcer went up to give Miguel the first place trophy, Miguel dedicated his victory to Johnny Lawrence and Cobra Kai.
However, Miguel and Hawk were both punished by Johnny for using a cheap shot to win and made to do 50 push-ups on their knuckles. Though initially still hung up over his break up with Sam, Miguel eventually began dating a new Cobra Kai student named Tory.
After Hawk attacked and vandalized Miyagi-Do and took Mr. Miyagi's medal of honor, Miguel fought Hawk to recover it so he could give it back to the dojo. After defeating Hawk, Miguel took the medal and went to the LaRusso residence to give it back, only to be greeted by Robby. Miguel handed Robby the medal and told him to let Sam know he had given it back, though rather than do that Robby simply dropped the medal in the yard and did not inform Sam that Miguel had returned the medal.
Later though, Miguel and Sam were able to make amends a party hosted by Moon after Aisha told Sam that Miguel had in fact returned the medal. Sam went to apologize to Miguel for not realizing he was the one who returned the medal and the two ended up kissing, which was secretly seen by Tory.
On the first day of school, Tory went to attack Sam for kissing Miguel. Miguel raced to get to the confrontation to stop her and came in just as Robby Keene had stepped in in an attempt to resolve the fight. However, assuming Robby was trying to harm Sam, Miguel tackled him to the ground. As the whole hallway erupted into fighting, Miguel fought Robby, who was angry at him for kissing Sam and believed he was taking advantage of her. The fight eventually led onto the second floor of the school where Miguel managed to defeat Robby and pin him down. Remembering a speech by Johnny to not confuse "mercy" with "honor", Miguel let Robby go and told him "I'm sorry". However, still bitter over Miguel kissing Sam, Robby attacked Miguel and knocked him over the railing, sending him plummeting to the ground below. The impact of the fall severely injured Miguel and sent him into a coma, necessitating him to be hospitalized.