The Champion Cartoonist Of All Time has got to be Windsor McKay. He created Little Nemo In Slumberland, Dreams Of A Rarebit Fiend, and Gerty The Dinosaur, to name but a few. He was one of the original pioneers of cinema and used to do a trick act where he performed live on stage as if he was training Gerty, who was actually nothing more than a filmed dinosaur.
Little Nemo is hours upon hours of fun for any kid of any age. McKay drew with architectual precision. He had full page panels that would work equally well upside down as right side up. His imagination knew no bounds.
We feel safe in saying that none of other hero drawers could do the work they have accomplished without him to pave the way -- so imagine how dull that world would be: No Miyazake, no Tex Avery, no David Weisner, no Chris Ware, and so on and so on and so on.
There is a great collection of his work on-line at the Comic Strip Library.