Boris Karloff
This was an interesting part for Mr. Karloff. Not that he hasn't played a loony before but that his part really had very little to do with the main plot of the movie! He was there as a red herring in a role where nearly any other actor could play the part.
Admittedly, he does add wonderful presence but still ...
Suppose I just think of him as a lead actor and seeing him in a throw-away like this is unusual. It's almost as if he took a couple days to film just for the cash (rent was due? ;) ) and went on to something else.