Karl Amadeus Mordo became a student of the Tibetan sorcerer known as the Ancient One. When Mordo plotted to kill his teacher, Dr. Stephen Strange learned of the plot. Mordo was forced to cast restraining spells to prevent Strange from warning the Ancient One. In desperation, Strange decided to accept the Ancient One's offer to take him on as his mentor in magic to have some hope of stopping Mordo. The Ancient One, however, was fully aware of Mordo's plot and of Strange's desire to warn him. Pleased at Strange's unselfish decision, the Ancient One's magical teachings immediately freed the doctor and explained the full situation. Thus informed in the face of his recent experiences, Strange agreed to become the Ancient One's apprentice despite the requirement that he abandon his former life. The Ancient One trained him to be a formidable opponent of Mordo. Eventually Mordo was exiled by the Ancient One. Mordo's abilities were similar to those of Doctor Strange, but Mordo was particularly skilled at astral projection and hypnosis, as well as mesmerism. Mordo was more than willing to use powerful black magic and invoke demons, both of which Strange was reluctant or unable to do. Mordo's use of these darker arts would sometimes backfire.
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History
CREATORS: Stan Lee, Steve Ditko
FIRST APPEARANCE: Strange Tales #111 (August, 1963)
THE LAST DAYS OF MAGIC
Mordo forces a family to leave their residence, but lets the mother stay as his servant. Dormammu incinerates the woman's body as he possesses her in order to chastise Mordo for delaying his plans. Mordo heads to the Sanctum Sanctorum and attacks Wong with Doctor Strange confronting him and the two briefly battle before the latter is taken by Nightmare. Mordo, angered that his foe was taken by another, is confronted by Dormammu again (in the form of a swarm of rats) who proceeds to attack Mordo causing him to leave. He later catches up to Doctor Strange when he is attacked by Orb, until Dormammu arrives. He then helps Doctor Strange in banishing Dormammu directly to Shuma-Gorath.
SECRET EMPIRE
During the "Secret Empire" storyline, Baron Mordo becomes the caretaker of Manhattan after it gets surrounded by Darkforce following Hydra's takeover of the United States. In addition to using the Sanctum Sanctorum as his residence, Baron Mordo has the Elder God Pluorrg guarding the Sanctum Sanctorum. He later catches Daredevil, Luke Cage, Cloak and Iron Fist when they are attempting to fight him. Mordo is then defeated by Doctor Strange, Spider-Woman, Ben Urich and Kingpin.