It was a secret the men who created Superman kept for 60 years and eventually took to their graves.
For all that time writer Jerry Siegel and artist Joe Shuster let people think they dreamed up the bulletproof flying avenger as a way to attract girls because they were a pair of 17-year-old wimps.
But now the comic world is abuzz because it seems the Man of Steel was really born from a personal tragedy.
Tragic origin: Christopher Reeve as Superman who creator Jerry Siegel may have come up with because his dad died after an armed raid
In 1932, just a year before Superman’s first adventure was tentatively drawn on a sketchpad, Jerry Siegel’s father, Mitchell, a poor Jewish immigrant, died during an armed raid at his second-hand clothing store.
The cause of Mr Siegel’s death is still shrouded in mystery.
His reclusive family appear to have believed for years that he was shot twice in the chest.
Modern researchers think the shots missed and he died of a heart attack.
But the death in Cleveland, Ohio, had a tremendous impact on his teenage son.
And in Superman’s first adventure Siegel and Shuster show him flying to rescue a bound and gagged shopkeeper who is being held up by a gunman.
There’s more, says best-selling author Brad Meltzer, who has researched the origins of one of the world’s most famous and enduring comic heroes.
Secret to the grave: Superman creators Jerry Siegel(left) and Joe Shuster never suggested the hero was created from a personal tragedy
The day after Mr Siegel died, as newspapers argued over the need for a vigilante force to protect ordinary people during the desperate days of the Depression, a letter to the Cleveland Plain Dealer denounced the idea.
It was signed L. Luther.
Mr Meltzer said: 'When I saw the first Superman illustration I thought, wow, is that Jerry’s alter-ego flying to rescue his helpless father?
'Then I saw the letter in the paper and wondered, could that be the origin of Lex Luther, Superman’s arch-enemy? Surely it can’t be coincidence.’
Yesterday comic experts agreed there is strong evidence to support the theory.
Arch enemies: Christopher Reeve as Superman with his arch-enemy Lex Luther played by Gene Hackman
In his earliest incarnation Superman’s greatest strengths were that he was bulletproof and could fly.
All his other powers, such as X-ray vision, came later.
The Superman creators can’t help.
Mr Shuster died in 1992, and Mr Siegel in 1996.
That first illustration dating from 1933, the oldest-surviving drawing of their hero, was never published.
It took the men six years to get their first Superman story in print and they spent the rest of their lives trying to regain the rights to their creation.
But comic historian Gerard Jones, author of Men of Tomorrow: Geeks, Gangsters and the Birth of the Comic Book, said: ‘There are clear similarities between Jerry’s early years and the fictional Superman’s flight from the planet Krypton.
‘Superman's invulnerability to bullets, loss of family, destruction of his homeland — all seem to overlap with Jerry's personal experience.
'There's a connection there: the loss of a dad as a source for Superman.'
Mr Meltzer said: ‘Think about it. Your father dies in a robbery, and you invent a bulletproof man who becomes the world's greatest hero.
‘America ... got Superman because a boy lost his father.'
Iconic: The first ever Superman comic book(left) and Brandon Routh in the latest film made based on the comic