With Great Power: The Stan Lee Story

Stan Lee:
I don't know what the universal conception of creator is. Steve definitely felt that he was the co-creator of Spider-man. That was really, and once he said it I realized that it meant a lot to him, that was fine with me. So I said, "Fine, I'll tell everybody that you're the co-creator." But that didn't quite satisfy him. So I sent him a letter, I put it in writing, To whom it may concern: This is to state that I consider Steve Ditko to be the co-creator of Spider-man, or something like that. And I said you can show this to anyone you want to.