The truest test of an actor's skill is not in resume or repertoire.
It is whether or not he/she can make me laugh so hard that I snort while improvising an impromptu monologue on a late-night television talk show.
Conan's done it to his guests, as has Craig Kilborn, and more notably, it is the only thing that is keeping Jimmy Fallon's show from going under.
Michael Emerson's rendition of Little Boy Blue ("he needed the money, oh!") on Jimmy Fallon's show comes to mind, as does
Sir Ian McKellen's Shakespearean lesson on how to change a tire on the
Late Late Show. And
Will Arnett reading from Are You There God? It's Me, Margaret gave me a chuckle—nay a full-fledged guffaw— today at work.
You want to be an actor? Start boning up on your monologue from
Alexander and the Terrible, Horrible, No Good, Very Bad Day.