Charlie Sheen is one part Jack Nicholson, one part Johnny Carson, shaken with a dash of "Chronicles of Narnia." So says Dana Carvey, anyway.
The former SNL star stopped in on Letterman on Monday and gave a pretty well deconstructed look at how one develops an impersonation of Charlie Sheen. Most impressions fall on a spectrum between certain iconic voices, so if you can do one or two, you can probably do more. All that's left after that for mastering Sheen is an encyclopedic knowledge of mystical creatures.