4. Adam Sandler - Punk Drunk Love (2002)
I know what you're thinking: this entry isn't a physical transformation the way the other entries on this list have been. Adam Sandler's career blew up in the early 1990's as a cast member of Saturday Night Live. He followed this up with successful comedy albums and low-brow goofball comedies like Billy Madison and Happy Gilmore. Famous comedians often transition into drama. Jim Carrey made the gradual transition by dipping his foot into the water's of dramedies like Truman Show before going full-out drama in Eternal Sunshine of the Spotless Mind. Bill Murray made a similar paradigm shift. Then there's Sandler. He went from Little Nick to Mr. Deeds to... a PT Anderson film about the burgeoning love of a lonely and troubled man? Unlike other Sandler films which did little to display actual acting chops, Punch Drunk Love is a complete actor-driven film, proving that there's more to the comedian than just debating the order shampoo and conditioner are used. Though not a physical transformation, Punch Drunk Love transformed the way audiences viewed Sandler.