I always saw Frank Gorshin's Riddler as a milestone in television drama. Up until then, bad guys in the movies and TV committed crimes... but sort of felt bad about it later. Movie directors were hesitant to show villians in a completely bad light, and the characters either decided the law didn't apply to them, or they justified their actions with rationalizations. The Riddler was different. Decades before amoral characters like in "Natural Born Killers," the Riddler was a person without any morals or conscience. Here was a bad guy who knew he was a bad guy and enjoyed it-- he had fun stealing things and hurting people.

As far as movie villians go, I would compare Gorshin's Riddler with Jimmy Cagney's character in "White Heat" or Powers Boothe's Jim Jones in "The Guyana Tragedy." They set the standard for movie bad guys that was hard to top.