There is no one who can be considered Dr. Strange’s rival, exception this guy. Introduced in Strange Tales #111 (1963) by Stan Lee and Steve Ditko, Karl Mordo is the son of Nikolai Mordo, a baron that wanted revenge after World War I, and Grandson of Viscount Heinrich Krowler. Growing up in a lonely life, Karl’s mother killed Nikolai on Krowler’s order and Krowler began teaching Karl the dark arts. Karl would learn the truth of his father’s death and swore revenge. Krowler would eventually send Karl to train with the Ancient One in Tibet. While an excellent but evil student of the Ancient One, Mordo discovered a book that allowed him to make contact with Dormammu. He summoned Dormammu who took over the body of Krowler’s body. A time-travelling Strange stop Dormammu, leaving Krowler with a broken mind and body. Mordo learnt of this and snuck home to reclaim his right as Baron Mordo. He returned to the Ancient One and continued his studies, wanting to overthrow the Ancient One, until a new student, Stephen Strange, exposed his plot and he was thrown out of the temple.

This would earn his hatred against the Ancient One and Dr. Strange, battling many times. When Strange was made Sorcerer Supreme following the Ancient One’s death, he would continue to battle Strange to wrench the role from his foe. He would also become a frequent minion of Dormammu but would fail every time being sent to a mystic prison. He was released when a group rescued him and formed the Circle Sinister. He would later join the Legion Accursed before discovering he had cancer. After trying several method for a cure, including selling a soul to many demons, he went to Tibet to seek forgiveness from all those he wronged, especially Strange, who did forgive him and allowed his rival to die in peace.

But of course, he wasn’t gone for long, because he would plucked out of time and forced to join the Offenders, the opposite of the Defenders, and made to fight their rivals one behalf of Collector and Grandmaster. They were all killed but were resurrected soon after. He was later revealed to be alive and during an encounter with Monet, was made to believe he was cured of cancer. He was later found dead by Kang with Thor’s ax in his chest only to be resurrected by Dormammu for his revenge against Strange. When New York was covered in the Darkforce in Secret Empire, he was appointed to the Sanctum Sanctorum to watch over the city. He was later one of many people suspected of killing Strange, only for it to turn out if was his assistant, Kaecillius. He then worked with Strange’s friends to hold back a demon attack.