There was once a list of top ten creepiest villains;
three of the stand outs were;
Bruce Dern from "The Cowboys"
Lee Marvin from "The Big Heat"
Richard Widmark for "Kiss of Death" with Victor Mature.
Widmark portrayed Tommy Udo, a giggling psychopath who pushed a wheelchair bound little old lady down multiple flights of stairs. It was Widmark's film debut after performing dramas on the radio.
I remember a drama teacher who once said;
"I saw Richard Widmark at my college and he was fantastic. He could drift in and out of character with ease. It is too bad he never made it to the big time."