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Poor Santa. He's a big guy and everyone knows it. He's probably the last person it's socially acceptable to describe as having a "belly like a bowl full of jelly.” We're not helping with his weight problem, either. On Saturday night, he'll be guzzling down a few million cookies and glasses of milk. This heavyweight Santa we know today has a much different body type than he used to. Most depictions of Santa's predecessors - Father Christmas and St. Nicholas - are 75 to 100 pounds lighter. When exactly did Santa put on all that weight?

A trim and fit St. Nicholas walking with Krampus on an 1899 Czech card.

Editorial cartoonist Thomas Nast - known as the father of the American cartoon - developed our modern image of Santa in the mid-19th century, beginning with an 1863 issue of Harper’s Weekly. Nast drew both the cover and a center-fold illustration, which paid tribute to the sacrifices of soldiers and their families during the Civil War. A noticeably more filled-out Santa is there to ease their plight with toys and Christmas cheer. Over the next few years, Nast's Santa got bigger and bigger, and other illustrators began drawing similarly pump Kris Kringles.

Nast didn't invent fat Santa out of whole cloth, though, and may have modeled his depiction after the titular character of “A Visit from St. Nicholas” (“Twas the Night Before Christmas”). The poem says that Nick had "a broad face and a little round belly/That shook, when he laughed like a bowlful of jelly./He was chubby and plump, a right jolly old elf/And I laughed when I saw him, in spite of myself." To be fair, it also described Santa as a "little old driver" in a "miniature sleigh pulled by eight tiny reindeer." In other words, he was sort of elfish, but still a fat elf. If Nast borrowed from the poem, though, where did its author come up with the idea for a fat Santa?

On St. Nicholas Day in 1809, Washington Irving published the satirical A History of New-York from the Beginning of the World to the End of the Dutch Dynasty, attributing it to fictional Dietrich Knickerbocker. The book was full of references to St. Nicholas, whom New York's Dutch founders would have called Sinterklaas. Irving didn't describe Nicholas as the traditional saintly bishop, but as a short, stocky guy in a low and wide brimmed hat smoking a pipe—a contemporary stereotypical image of a Dutch sailor.

Lest a Santa based on a parody of New York's Dutch culture and Dutchmen ruin your holiday, there may be an older influence, too. Central figures in some of the ancient pagan winter festivals of Europe, like the Holly King and the Oak King, bear more than a passing resemblance to Santa. Instead of poking fun at Dutch seamen, Irving's Santa may have been a conscious or unconscious re-fattening and re-paganizing of the Christian St. Nick.

The traditional European St. Nicholas, Washington Irving's Sinterklaas, and the twentieth-century American Santa Claus. From 1942's Santa Claus Comes to America (Caroline Singer and Cyrus Baldridge).