Which Actor's Appearance in a Film Surprised You the Most?

Which actor's appearance in a film did you find the most shocking? Who surprised you the most by appearing in "that kind" of movie? For example, choices could be a comedic actor doing a dramatic role or a Shakespearean actor in a slasher film or a dramatic actor singing in a musical.

Discuss here: http://www.imdb.com/board/bd0000088/flat/245302436