While there were already artistic images of St. Nicholas/Father Christmas/Santa Claus, the first time we saw the jolly old elf as a fat man with a pointed stocking cap was in 1863, in a political cartoon showing Santa celebrating Christmas with Union soldiers during the Civil War. He's playing with a toy effigy of Jefferson Davis in a cartoon that appeared in Harper's Weekly. In fact, how we think of Santa's appearance has a bit to do with how political cartoonist Thomas Nast himself looked.
In addition to repurposing the imagery of the Moore poem—reindeer pulling a sleigh, sack full of presents—Nast also found inspiration in his surroundings. He based Santa’s bearded visage and round belly partially on himself and used his wife and children for other characters, says Ryan Hyman, a curator at the Macculloch Hall Historical Museum. Located in Nast’s hometown of Morristown, New Jersey, the museum holds a large collection of his work. “The outside pictures that show rooftops and church spires were all here in Morristown,” Hyman adds.
Though they varied from year to year, Nast’s Santa drawings appeared in Harper’s Weekly until 1886, amounting to 33 illustrations in total. Unsurprisingly, the drawings from the Civil War often fell solidly in the realm of propaganda; Nast staunchly supported abolition, civil rights and the Republicans. But even after the war ended, Nast continued to use Santa Claus to make certain pointed political statements.
Even the most familiar of Nast's illustrations of Santa Claus has political symbolism that has been lost over time. Read about Nast's Santa drawings at Smithsonian.