Robin Williams' 'Set List' Appearance Is Amazingly Funny (VIDEO)

The premise behind Set List, the uniquely innovative comedy show hosted by Paul Provenza (director of "The Aristocrats") and created by Troy Conrad, and developed with Provenza and Barbara Romen is simple: Words are projected on a screen, and stand-up comedians have to improvise jokes based on the words. It's a thrilling and exhilarating way to see a comedian test his or her chops without a safety net.

Dropping into the show recently was Robin Williams. It's easy to forget that although he's become a wildly successful actor, Williams got his start as a stand-up comedian, and it's clearly an art form he still loves. His appearance on Set List could be his funniest performance in years -- watching the flashes of inspiration appear on his face as he builds a new character or joke right in front of the audience's eyes is mesmerizing.

Check out the clip above to see Williams make up a stand-up set on the fly at NerdMelt in Los Angeles.