Maximilion Pegasus is the brilliant and eccentric creator of the Duel Monsters card game. In the events of the film, which take place after the Battle City tournament, he is sought out by Seto Kaiba, who believes that Pegasus must have created a card capable of countering the Egyptian God Cards. Pegasus agrees to give Kaiba such a card if he can defeat him in a duel. He loses the duel and hands over two cards, one of which was secretly planted by the ancient evil Anubis. Later, Pegasus deduces that a dangerous Shadow Game is unfolding. He arrives by helicopter to rescue Tea Gardner, Solomon Muto, and Mokuba Kaiba from the collapsing Duel Dome, using his knowledge of the situation to aid the others.

Pegasus is sophisticated and cultured, presenting himself as a perfect gentleman with a theatrical and overly dramatic demeanor. He is obsessed with cartoons, which inspire his Toon monster cards, and he often addresses others with the suffix boy, as in Yugi-boy or Kaiba-boy. Beneath this flamboyant exterior, he is a shrewd businessman and a skilled duelist who used to abuse the power of his Millennium Eye to read minds. By the time of the movie, he has largely abandoned his earlier ruthless ambitions, having already redeemed himself after his defeat in the Duelist Kingdom arc. His core motivation has always been a deep longing to reunite with his deceased lover Cecelia, but that personal quest is not directly evoked in this story.

In the film, Pegasus is not the antagonist but a former adversary turned neutral party. His key relationship is with Kaiba, whom he treats with amusement and respect as a worthy opponent. He also shows a courteous, almost paternal concern for Yugi and his friends. His main development in the movie is his willingness to intervene and help, demonstrating that he is a man of his word and capable of genuine heroism. Pegasus possesses notable abilities: his Millennium Eye grants him limited telepathic powers, and he is an expert duelist. His signature deck relies on Toon monsters and direct attacks, though in his duel against Kaiba he is defeated after a brief clash, partly because Anubis secretly tampered with his deck. Later, his quick thinking and knowledge of the arcane make him instrumental in ensuring the safety of the bystanders.