Oscar Diggs, a circus magician from Omaha, Nebraska, became known as the "Magicien d'Oz" after a storm swept his hot air balloon into the Land of Oz. Finding the realm leaderless and threatened by powerful witches, he adopted the identity of a mighty wizard to impose order through fear and elaborate illusion. He ruled the Emerald City, using props and magic tricks to manifest terrifying forms—a giant head, a beautiful lady, a monstrous beast, or a ball of fire—reinforcing his image as "Oz the Great and Terrible." His reign depended on the belief that only a powerful sorcerer could protect Oz from the Wicked Witches.

When Dorothy Gale and her companions sought his aid, he demanded they eliminate the Wicked Witch of the West as payment. After their success, Dorothy's dog, Toto, exposed him as an ordinary man operating behind a curtain. Diggs confessed his origins, explaining his illusions were meant to shield Oz from chaos. To symbolically fulfill his promises, he gave the Scarecrow a head filled with bran and pins representing a "brain," the Tin Woodman a silk heart stuffed with sawdust for a "heart," and the Cowardly Lion a potion for "courage." Recognizing their inherent qualities, these tokens helped them perceive their own strengths. He then attempted to return Dorothy to Kansas using his hot air balloon, appointing the Scarecrow ruler of the Emerald City in his absence. The balloon departed prematurely when Dorothy chased after Toto, leaving him unable to help her further.

His legacy in Oz endures as a figure whose deception inadvertently stabilized the realm, with later rulers referencing his actions. His role is defined by his backstory as a stranded showman and his pragmatic, dishonest approach to governance.