Medina was a 23rd century Starfleet lieutenant serving aboard the USS Constitution as a relief helmsman in the late 2250s. In 2257, Medina was called to the bridge to relieve Lieutenant James T. Kirk at the helm console so that he could assume command after Captain Augenthaler and Commander Akira Hirota beamed down to Sordinia IV. Medina remained at his post for the majority of battle with the N'shaii mothership, but was knocked unconscious after the Constitution was hit by a muon burst. Medina was later taken to sickbay with a suspected head injury. (TOS - My Brother's Keeper novel: Constitution)