Warning: contains spoilers for Thor: Lightning and Lament #1!
Marvel's Jack Kirby's Thor was a success - but Steve Ditko decided to alter the origin of his own magical doctor for a very important reason.
Thor was created in 1952 with the release of Journey Into Mystery #83. Written by Stan Lee and Jack Kirby, the issue chronicles the tale of Donald Blake, a brilliant medical doctor who finds a mysterious staff while trapped in a cave during an alien invasion. The staff turns into the legendary hammer Mjolnir, and Donald Blake transforms into Thor: the Norse God of Thunder with incredible power. This echoes the origin of Doctor Strange, also a brilliant medical doctor - but unlike Thor, Strange found power through his own failings.
In Thor: Lightning and Lament #1, written by Ralph Macchio with art by Todd Nauck, Thor recounts his earlier adventures in which he balances his life between his medical practice as Donald Blake and his time as a superhero and an Avenger. "The warrior and the healer...embodied in one being..." muses Thor/Blake. While this aspect of Thor's backstory isn't visited as often as it used to be, it is a key aspect of Doctor Strange, but his days as an expert surgeon are over thanks to Ditko's key addiction to the origin story.
In Doctor Strange's first appearance, he was seen as an arrogant doctor who refused patients simply because he did not want to take a chance on their problematic illnesses. Losing the use of his hands in a horrific car accident, Strange turned to the mystic arts and eventually became the Sorcerer Supreme. Creator Steve Ditko perhaps thought Thor's origin didn't give him any flaws - and when Odin revealed that Blake was Thor and had brought him to Midgard to teach him humility, his memories were altered. If Blake's memories of his time as Thor were changed, how could he ever learn the errors of his early ways?
Thus, Steve Ditko gave Doctor Strange a character flaw - his hubris - and allowed him to said flaw so he could improve as a person. It's possible that Ditko created his own medical-into-magical character to one-up Jack Kirby's creation to win favor with Stan Lee. Nevertheless, Thor and Doctor Strange's origins are similar, but the Sorcerer Supreme has the stronger beginning owing to an important lesson learned about his own ego.
