One of the genetically engineered followers of Khan Noonien Singh, revived from the sleeper ship Botany Bay in 2267, who helped seize the Enterprise and struck Uhura on the bridge.
Joaquin appears in the episode Space Seed. A powerfully built survivor of the Eugenics Wars, he is among the men and women Khan awakens from suspended animation once he has stolen the Enterprise's technical manuals and slipped back to his ship.
He acts as Khan's right hand during the takeover. With the bridge crew captive in the briefing room, Khan orders Uhura to work the viewscreen so that all can watch Kirk suffocate in the decompression chamber; she refuses, and Joaquin hits her across the face.
He is overcome with the others when Kirk and Spock flood the deck with gas, and goes into exile with Khan on Ceti Alpha V. A very similar lieutenant named Joachim appears in the film Star Trek II. Joaquin was played by Mark Tobin.