History
Mordo was believed to have been studying under the Ancient One a good share of his life. However, Mordo grew arrogant after several battles, and delighted in his prowess as a warrior rather than sticking to the Ancient One's rule that his sorcerers are guardians, not warriors. Angered by Mordo's arrogance and aggression, the Ancient One sought out Strange to initiate him into the role of Sorcerer Supreme. However, he discovered Strange too struggled with pride. Yet, Strange's source of his pride and bitterness was easier to deal with, than with Mordo's arrogance. After realizing that Strange, in spite of everything else about him, did not actively seek the title of Sorcerer Supreme to succeed the Ancient One, it was deemed that Strange's new-found humility made him a suitable heir for the title.
Mordo learned of the Ancient One's plans to promote Strange to Sorcerer Supreme, and was soon overcome with jealousy. Outraged and having felt betrayed by the Ancient One, Mordo defected and formed a pact with Dormmamu to seek his revenge on the Ancient One and Strange. However, Mordo's plans were short-lived, when Dormmamu devoured him after he grew impatient with his inability to defeat Strange in battle.[1]