Joaquin is a computer science student at Chicago Polytechnic University and close friend of Phillip Gallagher. Joaquin comes from a lower class background and goes to school on scholarship. He was also accepted to Stanford University but turned it down because California is too hot for him.
Joaquin is one of the students who unknowingly buys synthetic marijuana from Kev, and he breaks his leg after jumping out of Lip's dorm room window while suffering a bad high from the drug. When Lip visits Joaquin in the hospital, Joaquin acts like he told the police where he got the drugs to mess with Lip, but ultimately reveals that he did not tell anyone where he got them.
In Season 7, Joaquin helps Lip commit wire fraud by wiring money from Lip's unpaid internship to a separate account. Joaquin and Lip justify it because the company does not pay interns despite making a lot of money and hiding it from the FBI.