Here is my nomination.
I would disqualify old Chuck, because he's an actual person. A cartoon, inherently, has never existed in reality!
Player: "That's checkmate, Judge"
Dredd: "That's ten years in the Juve cubes, Perp... I am the Law!"
I'd have to say Betty Boop, based on the cartoon at the following link. However, I guess I should mention that during this cartoon poor Betty has several wardrobe malfunctions, and, worst yet, is molested repeatedly by a very bad king. So, kids, I know the link is below, but don't click on it. It's a very, very nasty cartoon. There's a reason why it doesn't appear on TV anymore.
http://www.youtube.com/watch?v=Lw3LU5a7Z8Q
Which cartoon character would be the best chess player? I think Patrick from SpongeBob Squarepants would be the most intimidating player.