Baron Mordo plots to defeat the Master and learn his secrets so that he can become stronger than his rival, Doctor Strange. In his spirit form, he travels to Tibet and forces the servant to put poison in the Master's food. When the old man is vulnerable, Mordo tries threatens him to reveal his secrets of black magic or his potion will suck the life away from him. Doctor Strange arrives and uses his amulet to revive the Master. With Strange threatening Mordo's physical body, he brings back his spirit form to it to protect it, but the move breaks his control on the servant and the Master is saved.

Mordo met Dr. Strange for the first time when the famous surgeon came to India to ask the Ancient One to heal the injuries to his hands. While Mordo secretly attempted to kill his master by summoning the dark magic of Dormammu, he was surprised by the visitor and used a spell to keep him silent on that matter.

After his disciples have failed their attack on Doctor Strange, Mordo materializes before him and tells him that he has captured the Ancient One. They engage in a mystic battle where Doctor Strange goes around the world from one location to another until he has found where Mordo has hidden his old mentor. Dominating his opponent with his spells, Strange forces him to free the Ancient One.

Impersonating Sir Clive Bentley, Baron Mordo lures Doctor Strange to London and entraps him. With the help of Victoria Bentley, who has latent skills for magic, Strange is set free, and finding that he is no match for his opponent's mystical abilities, Mordo leaves the place.

Baron Mordo makes another attempt on the Ancient One's life but Doctor Strange stops him.

While Doctor Strange travels in astral form, Baron Mordo steals his physical body and hides it in a wax museum. Strange tracks it down and forces Mordo to leave his body so he can recover his own.

Dormammu provides Baron Mordo with limitless powers so that he can destroy Dr. Strange. With two of his disciples, he travels to the Ancient One's sanctum in Tibet and attacks Dr. Strange and his mentor, forcing them to flee. Mordo locates his enemy in Hong Kong, but despite his resources, he target eludes him. Finally, he learns that Strange has activated the Orb of Agamotto in his sanctum so teleports there to engage in combat. After Strange fades away in combat, Mordo reports his victory to Dormammu who replies that their foe simply escaped to another dimension. Learning from a wraith that Strange was back, traveling in his ectoplasmic form, Dormammu sends Mordo and his wraith after him. Suddenly, Dormammu is forced to interrupt his power support. As Dr. Strange spirit heads for the core of the sun, Mordo decides to wait until the magician gets back on Earth and Dormammu has restored his powers.

Sir Baskerville, one of Mordo's disciples, warns his master that Dr. Strange has arrived in London asking about Eternity. He instructs Baskerville to stall the magician while he sends another disciple to deal with him. But Dr. Strange suspected the trap and knocks the disciple down. Then Strange convinces Mordo's wraiths to seek for him in the Netherworld. Mordo orders his followers around the world to keep an eye out for Dr. Strange. Then he strikes the most knowledgeable mystics with a spell of silence to keep them from speaking about Eternity. Yet, each time they manage to locate Strange when he casts a spell, Mordo arrives too late to catch him. During Strange's quest to Eternity's world, Mordo travels to Tibet where he kidnaps the Ancient One and takes him to his sanctuary where he hides him in a time trap. Then the fight begins, and Mordo asks for more and more power from Dormammu as he gets closer to victory. But Strange's clever tricks anger his opponent and make him reckless, so Dormammu decides to take over. He sends Strange, Mordo and the Ancient One to a neutral dimension where he summons the rulers of neighboring dimensions to witness the final combat. As Strange gains the advantage in the physical fight, Mordo decides to act and takes him down with a spell. Angry at Mordo for this unwanted intervention, Dormammu exiles him to the Dimension of Demons. Dr. Strange then convinces Dormammu to resume the fight and defeats him.

With Dormammu reduced to nothingness during his clash with Eternity, his spells are lifted and Mordo emerges from his exile. The Ancient One decides to hold him prisoner until he has reformed.