El Mariachi is the guitar player, and the main character in the films El Mariachi, Desperado, and Once Upon a Time in Mexico.
In El Mariachi he is played by Carlos Gallardo and in Desperado and in Once Upon a Time in Mexico he is played by Antonio Banderas.
El Mariachi's adventure with criminals begins in El Mariachi when he arrives in Acuna, Coahuila, Mexico, which is "owned" by a drug dealer, named Moco, who is looking for another man in black (El Mariachi wears black), and carries a guitar case; which is full of machine guns. Only Moco knows what he looks like, and the desciption was very simple, which led them thinking El Mariachi was man they were looking for, and go on a mission to kill him.
Mariachi shoots many of Moco's men, in self defense. Suddenly he is captured by one of the men and thrown into his pickup truck, beaten, and taken to Moco's ranch. The men realize their mistake when Moco tells them it's not the one that was being sought for, and is let go.
Later, El Mariachi ends up back at the ranch when his newfound girlfriend, who Moco wants to be girlfriend with badly, is held captive. He gets shot in the hand by Moco, so he can't play the guitar anymore, when he finds out about their relationship. In revenge, Mariachi picks up a revolver and shoots Moco, killing him.