Tom Kenny: the titular, forever-cheery main character SpongeBob SquarePants - as well as one of the most tragic characters in kids cartoon history as The Ice King in Adventure Time.
When you need a celebrity impersonator, you call up Maurice LaMarche. His Orson Welles might be better known as Animaniacs' The Brain, which is pretty much the same voice. In addition to Brain (and Futurama's long-suffering Kif Kroker), he's also voiced:
Frank Welker is possibly the most legendary living voice actor - particularly because of his incredibly rare skillset of being able to do amazing voices for people AND animals (and pretty much anything else you can imagine). Abu from Aladdin and the screeching Maritans of Mars Attacks! barely make up a percentage of his work, which includes: