Far from being the most recognized superhero ever conceived, Birdman shows a very clear illustration of how television cartoons have evolved. All one has to do is compare the character's initial run (1967-1969) with his return to television in 2000.

John Michael Higgins isn't a household name, but you've probably seen him acting in Christopher Guest films and/or as Wayne Jarvis on Arrested Development. He also portrayed Letterman in The Late Shift, something he says Letterman still hates him for.