Also parodied was My Greatest Adventure, the title the Doom Patrol originally appeared in. Part of a long string of fictional characters "come to life" in Morrison's writing, Flex was apparently created by a psychic child with a green pen. The characters created in this child's youthful scrawlings, titled "My Greenest Adventure", apparently came to life. Amongst Flex's "Greenest Adventure" siblings were the villainous Waxworker and the heroic Fact.
In 1996, Flex Mentallo received his own four-issue mini-series written by Morrison and illustrated by Frank Quitely. Although ignored by the Charles Atlas company at the time, it was later brought to the company's attention by a fan of the comics. Charles Atlas company president Jeffrey C. Hogue was unhappy with its likeness being used this way, and filed a trademark infringement suit against DC Comics. DC submitted a motion for summary dismissal, which was granted on the basis of fair use using the parody defense. DC has so far declined to reprint the mini-series - although his initial appearances are included in DC's third and fourth collections of the Morrison Doom Patrol stories, "'Down Paradise Way" and "Musclebound".
When Flex was still a "mac" instead of a "man", he was bullied a lot while on the beach. Tired of being scrawny, he was approached by a man with a TV for a head and smoked three cigarinos at a time. He gave Flex a coupon to fill out to get a body building book, "Muscle Mystery for You". The instructions in the book turned Flex into the muscled strongman he is now, and he learned that when he flexed one type of muscle, he could alter reality. As he did, his "Hero Halo" appeared over him, which read "Hero of the Beach". After this, he decided to become a crimefighter and dressed in wrestling boots and leopard-skin trunks.
Flex teamed up with a group of heroes, the Zipper, the Atomic Pile, Dr. 45 and his assistant Romantic Rick, and the Fact. Strangely enough, he hinted, all their adventures revolved around the color green.
In 1956, while judging a swimsuit competition, Flex fell in love with and later married a woman named Dolores Watson. He was then approached by a reporter named Norman Grindstone, who was investigating the disappearance of detective Harry Christmas. Harry was "on to something big", as Norman put it, involving the Pentagon, a rash of 32 mysterious disappearances since 1949, silver sugar tongs, and an Ant Farm. Norman found Harry's conclusion about what was going on, and showed it to Flex. Both were horrified by Harry's discoveries. Soon after, Norman Grindstone was seemingly erased from existence. For two months Flex flexed about every muscle in his body to try and turn the Pentagon into a circle. Dolores left him in this time because he wouldn't stop flexing. He failed, and investigated the Pentagon up close. He was captured, however, by the (real) Men from N.O.W.H.E.R.E. and placed inside the Tearoom of Despair. Once there, he lost his powers and his memory, and was left to wander, homeless and crazy, until he found Danny the Street.
Flex eventually remembered the 32 disappearances; their number, he said, was 5, the number of sides of the Pentagon: "3+2=5 and that is their number. It is the number of anguish". After regaining his memory, he was reunited with Dolores, who returned his costume but then withered away; her parting words were "I love you. They made me." As she said this, the Men from N.O.W.H.E.R.E. suddenly stood in her place. They kidnapped Flex and young psychic Dorothy Spinner, bringing the two to the sub-sub basement of the Pentagon,to power the mechanical monstrosity Flex had discovered all those years ago: The Ant Farm.
While given a tour of the Ant Farm by the demented Major Honey, Flex learned that he was created by a psychic named Wallace Sage inside a comic book Sage created with green ink when he was a child called "My Greenest Adventure". Sage, along with Dorothy, was kidnapped as a means to summon the Telephone Avatar, a being that has enslaved the dead and haunted the telephone system for 50 years. The Doom Patrol soon invaded the Pentagon in an attempt to rescue Flex and Dorothy; in the confusion, Flex freed Wallace, who died within minutes. Upon Wallace's death, Flex regained his powers and successfully transformed the Pentagon into a circle, but he couldn't destroy the Avatar. The Avatar was eventually destroyed by the The Candlemaker, an entity that had been imprisoned within Dorothy's mind.
Flex went on to star in a four-issue miniseries in its own continuity.
When Flex uses his power, his "Hero Halo", a shimmering projection of the words "Hero of the Beach", appears above his head.