“Steve said, ‘Having an idea is nothing, because until it becomes a physical thing, it’s just an idea,’ ” Lee recalled. “And he said it took him to draw the strip, and to give it life, so to speak, or to make it actually some- thing tangible. Otherwise, all I had was an idea. So I said to him, ‘Well, I think the person who has the idea is the person who creates it. And he said, ‘No, because I drew it.’ Anyway, Steve definitely felt that he was the co-creator of Spider-Man. And that was really, after he said it, I saw it meant a lot to him that was fine with me. So I said fine, I’ll tell everybody you’re the co-creator. That didn’t quite satisfy him. So I sent him a letter.”
Text from Marvel Comics: The Untold Story.