Mariachi is a bounty hunter and a practitioner of The Old West. He loves his culture, his identity surrounded by it, donning the name 'Mariachi' for his keen interest in flamenco and various Mexican music. He grew up in a family of bandits, outlaws which would take various heists and stick-ups. 

He grew conditioned to the sound of their music, associating it with the beauty of violence and combat. Eventually times would change, and his family would get wiped out one by one. Some fled, others died, but he tried to stay for as long as he could, knowing no other life. Soon the civil war would come by, and he would join the rebellion.

Numerous times, he would be squared up against gunslinger legend Ned West, the two forming a rivalry during the war, at times even working together. But once the war was ending, Mariachi knew he wanted something else in his life for once, finding love with a woman. He escaped a raid on his compound, not telling a soul that he was settling down to have a family.

Mariachi settled into the quiet life, taking up music, unknowingly triggering his need for violence. Fearing what could happen, he took his old guns up, and left his family, settling back into his life of crime.

 Mariachi found money in taking things of high value from the UNSC, whether that was information or VIP targets. But soon, his luck would turn for the better, finding a lead on a data chip worth millions, enough to leave behind for his family for the day he dies.

Mariachi isn't much of a talker, although he understands English, he never likes to speak it, feeling at home by speaking his native tongue. While he is stern and antisocial, his combat style tells a different tale, a fighter who moves to the flow of the music in his head.

Note - Mariachi speaks Spanish almost all the time. Voice actors would need an understanding of dialect or are willing to do minor research