That was the question posed by Patt Morrison of the Los Angeles Times and it led to this answer:
Oh, no, if I didn’t like it, I wouldn’t have written it. Wait a minute, there was one. Jack Kirby and I were doing the Fantastic Four. We needed a new villain — we always worked under tremendous deadlines; we were doing dozens of books a month. I said: “Jack, I think a great name is Diablo; why don’t you draw a guy called Diablo, and we’ll give him some kind of power.” And he drew a real scary-looking guy, but I had no idea who Diablo was or where he came from. I must have batted out something and Jack drew it, and to this day I can’t remember what the Diablo story was. The only thing I ever wrote that I don’t know what it was! So I think I didn’t like that particular issue.”