T-Bone's background and real forename is unknown. At some point prior to 1992, he joined the San Fierro Rifa and eventually became the leader. Under his leadership, the Rifa confronted the Varrios Los Aztecas, Mendez himself killing two of Cesar Vialpando's friends.
By 1992, Mendez had become one of the three members in the Loco Syndicate, along with Mike Toreno and Jizzy B.. Mendez became the enforcer and protection of the syndicate, with Toreno overseeing and Jizzy arranging deals. T-Bone is a muscular man and very distrustful of others, nearly to the point of paranoia. He is seen beating a man to death during The Introduction machinima.
He and Carl Johnson meet for the first time during the mission T-Bone Mendez, and in the mission Mike Toreno, Carl drives while T-Bone uses his cellphone to locate Toreno. Mendez shortly afterwards becomes distrustful of Carl, and ambushes him from the back seat of a car in Outrider, holding a gun to his face and accusing him of being a "snitch", but his attempt to scare him into admitting it is unsuccessful.
Mendez's next and final appearance is in Pier 69. Carl by that point had turned against the Loco Syndicate and had already killed Jizzy B, so to stop the spread of crack cocaine into Los Santos by disrupting the syndicate's partnership and deal with Big Smoke's Crack Empire and the Los Santos street gangs. With the help of Cesar, Carl kills many Rifa and Ballas thugs. The pair both shoot Mendez at the same time, whose lifeless body falls over the edge of the pier and into the ocean below.