Medina began his career illustrating such titles as Berserker and Megaton at Megaton Comics. He subsequently worked for First Publishing, on such titles as Dreadstar and Hammer Of God in the late 1980s, before starting to work for Marvel Comics on The Incredible Hulk, Warlock and the Infinity Watch, Blackwulf, Avengers, The Amazing Spider-Man, and Marvel Knights Spider-Man.