Despite the inaccurate claims made by Coca-Cola for a number of years (they have since modified their story), and some confusion from other quarters, American illustrator Haddon Sundblom did not create the look of Santa Claus as we know him.
That story is a bit less than straightforward and involves a number of other illustrators, including Thomas Nast, J.C. Leyendecker, Reginald Birch, Norman Rockwell and others (see my post on Illustrators’ Visions of Santa Claus).
However, Sunblom, one of the great illustrators of the early 20th Century, refined the image of the character to his most recognizable form. Sundblom’s series of Santa illustrations for Coca-Cola ads, that ran from 1931 to 1964, gave us the quintessential modern interpretation of the Jolly One.
The Coca-Cola page has a selection of some of the images and the Coca-Cola Art blog has another page here, both with links to larger versions. An even better resource is the post on Golden Age Comic Book Stories, with many of the Sunblom Santas in one place (again, click for larger images). There is also a post on KoiKoiKoi.
Leif Peng has an excellent post on Sunny’s Santa on his blog Today’s Inspiration, and has a wealth of other posts on Haddon Sundblom. (Note: some of them include Sundblom’s pin-up illustrations, which can be mildly NSFW.)
I wouldn’t mind a lump of coal in my Christmas stocking if it was painted by Haddon Sundblom.