Finding Mary Marvel's Good Deed Ledger, the man who became known as Uncle Marvel read its contents and discovered the secrets of the Marvel Family. Taking the book back to Mary, he explained that he was her long lost uncle Dudley from California. When they both said, "Shazam!" Mary and Uncle Dudley were changed. However, unknown to Mary, Dudley had merely slipped out of his outer clothes and was already wearing a costume underneath.
Dudley then set up a business, Shazam Incorporated, naming himself the president, explaining that he would donate the proceeds of money paid for the Marvel's work to a good cause and that it would be a non-profit making venture. Mary soon realised he was a fraud when he said, "Shazam!" and did not change. But none of the Marvel Family said anything and let him continue his charade.
Uncle Marvel often begged off when he was supposed to fly by claiming he had "Shazam-bago." He once used a collapsible rocket motor - his own invention - to fly, but it didn't work properly and it was soon abandoned. It appears that Dudley is his last name, as he has a niece called Mary Dudley (Freckles). Although she sometimes wore a Mary Marvel costume and called herself Freckles Marvel, she never pretended to have any Shazam powers and is not regarded as part of the Marvel Family.
Following the Crisis on Infinite Earths, Dudley appears as a janitor at the school Billy Batson attends. Dudley is the one adult Billy confides his living situation with, namely that he lives on his own. Because of this, Dudley frequently covers for Billy on the frequent times he is tardy. Dudley also confides in a much bigger secret to Dudley after saving him from a heart attack: That he's the super hero Captain Marvel.
Later, Dudley takes Mary's Tawky Tawney doll (really a pooka in the form of a doll) out drinking. Following this, a drunk Dudley follows Mary back to the Rock of Eternity, where they revive Ibis the Invincible to combat the Seven Deadly Enemies of Man that Blaze has unleashed. Ibis gifts Dudley with temporary Marvel powers, allowing him to fight alongside the Marvel Family as a real member for once. Following this, he allows his powers to be taken away- he finds himself not suited for the superhero business.
Uncle Marvel appeared alongside the rest of the Marvel Family in The Kid Super Power Hour With Shazam! voiced by Alan Oppenheimer.
He also appears in episode 14 of the Young Justice series "Alpha Male" voiced by Corey Burton.