Originally Posted by zbinks
I think it was Karloff.
That's right. Karloff didn't want to tarnish the image of Frankenstein by appearing as the monster in a comedy. Physically I don't think he could do it anymore due to all the back issues the part caused him in the past. I know that Karloff was part of the publicity of the film since he was still under contract with Universal. Still I could have sworn that Lugosi and/or Chaney also had reservations about their roles in the film.