Senior Chief Petty Officer Franklin Mendez is a retired member of the UNSC, and was the lead trainer for both the Spartan-II and Spartan-III programs. He is highly decorated for his service, both during the Insurrection and the Human-Covenant War. He was known by all Spartan candidates as a very tough instructor, regularly putting his Spartan trainees in difficult scenarios that required them to discover what the trick of the situation was before they could successfully complete their mission.
While completing training of Spartan-III Gamma Company in 2552, Mendez, along with Kurt-051, Team Saber, Tom-B292, Lucy-B091, Catherine Halsey, and most of Blue Team became caught in the Onyx Conflict, where they managed to escape the Covenant by using a Forerunner slipspace bubble to travel to the Sarcophagus, albeit at the cost of Kurt-051’s life. The remaining Spartans, Halsey, and Mendez were eventually rescued by ONI covert unit Kilo-Five, though Halsey was arrested for her involvement with the Spartan-II program. Mendez retired after this, though he eventually returned to the Sarcophagus and became head of security for the research teams on the shield world.