A friend of mine, Alex Robertson once told me that the only believable villain for him in the BATMAN 66 series was The Riddler and that was because you got the sense from Frank Gorshin's performance that this guy was capable of anything. That at any moment, he could say "Fuck This" and open up Adam West's chest cavity with a Bowie knife.
That commitment as an actor bled into his work as an impressionist. While being strong vocally, he had a gift for turning his face into a mobile 3D version of an Al Hirschfeld caricature. As you could see in the above clip, he could contort his face from Burt Lancaster's broad Cheshire Cat grin to Kirk Douglas' seething intensity in a heartbeat.
And let's face it, any guy who can make a meal out a a host of bad riddles, deserves our respect. That giggle deserves to echo for a long time.