Santa Claus might be a thin, disagreeable character in a stiff-brimmed hat if not for the 19th-century cartoonist Thomas Nast.

Nast, from whose pen also came the Democratic donkey and the Republican elephant, gave Santa his present shape - short, fat and jolly man with a stocking cap and a long white beard - as a morale booster during the Civil War.Previously, Santa Claus was sometimes depicted as tall, thin and domineering, and often had black hair and a stiff-brimmed hat, said James I. Robertson, a history professor at Virginia Tech in Blacksburg.

"There was no stereotype of Santa Claus at that time," he said. "He tended to be in all shapes and sizes."

Nast, as a 21-year-old artist at Harper's Weekly in 1863, drew a short, fat, bearded Santa bringing gifts to Union troops in a star-spangled jacket, a cap and striped pants, Robertson said.

"The drawing boosted the spirits of soldiers and civilians alike because it showed the spirit of Christmas had come to the Civil War," the professor said.

Nast was influenced by Clement Moore, whose 1823 poem "'Twas The Night Before Christmas" depicted a twinkly-eyed, white-haired Santa smoking a pipe, the professor said.