Flex Mentallo is a fictional character appearing in American comic books published by DC Comics. Created by writer Grant Morrison and artist Richard Case in 1990, during their run on Doom Patrol. Flex is in part a parody of Charles Atlas' long-running "The Insult that made a Man out of Mac" advertisements seen in American comics from the past. In 1996, Flex Mentallo appeared in a self-titled, four-issue miniseries written by Morrison and illustrated by Frank Quitely. The miniseries forms part of what Morrison calls a thematic hypersigil trilogy along with The Invisibles and The Filth.