The Mendez Cartel was a very powerful drug cartel operating out of Vice City in the early 80's, until 1984. They arrive in Vice City around the same time as Victor and supply drugs to numerous high ranking officers at Fort Baxter. The Mendez Cartel also owns the mansion on Prawn Island that is eventually taken over by the Sharks in between 1984 and 1986. It is never disclosed whether they are related to San Fierro Rifa gang leader T-Bone Mendez; it could be a coincidence they share a last name. After Victor Vance kills Diego and Armando Mendez, the Cartel effectively ceased to exist.
In Vice City Stories, the only game they appear in, Mendez Cartel members are depicted as wearing suits, with light colored shirts underneath, as well as having a notable moustache.