Flex Mentallo is a comic book character created by Grant Morrison during his 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.