A 1990 article from the Comics Journal has artist Jack Kirby claiming he created Spider-Man. Here is the direct quote.
GROTH: Can I ask what your involvement in Spider-Man was?
KIRBY: I created Spider-Man. We decided to give it to Steve Ditko. I drew the first Spider-Man cover. I created the character. I created the costume. I created all those books, but I couldn’t do them all. We decided to give the book to Steve Ditko who was the right man for the job. He did a wonderful job on that.
GROTH: Did you know Ditko?
KIRBY: I knew Ditko as well as any man could. Ditko is a withdrawn, silent type.
GROTH: Did you guys get along well?
KIRBY: I got along with him. I can only speak for myself. I liked Steve very much.
ROZ KIRBY: We bumped in to him three years ago in New York.
KIRBY: He surprised me. He was very sociable, and we socialized, and he’s very open with people now.
GROTH: What kind of guy was he?
KIRBY: He was a very withdrawn guy. I never bothered him because I felt that that’s the way he wanted it. I talked to him when it was necessary. I believe that Steve was a kind of guy that wanted it that way. He was a wonderful artist, a wonderful conceptualist. It was Steve Ditko that made Spider-Man the well-known character that he is.
GROTH: Do you like his work?
KIRBY: Yes, because it’s got a definite style that you could recognize anywhere. You can point to any picture that Steve makes and say, Ditko did that. It’s individual.
ROZ KIRBY: They all look Polish.
KIRBY: Yeah. All his characters look Polish! [Laughter.]
What do you think of this old interview? The Kirby heirs recently lost their copyright lawsuit against Marvel/ Disney.