Don Rickles

definitely could've had a career playing evil heavies (see also X, The Man With X Ray Eyes) but then he got into comedic roles in the Beach movies (Big Drag, Big Drop, Jack Fanny)

For early 60s hokey scenery chewing, he could do the job for sure. "Good actor"? Nah, not so much.

I've never cared for his comedy. However, I've always thought that he was a better than average actor. Especially in dramatic roles. Another good example of a comic being a fine actor was Frank Gorshin. Are you familiar with any of his work?