Where did the image "Uncle Sam" come from?

During the 19th Century, a meat packer named Sam Wilson sells preserved beef to the U.S Army. The packs of beef meat were stamped "U.S" to indicate that they were the properties of the United States. However, the soldiers joked the "U.S Stamp" as the initials of the supplier, "U-ncle S-am" Wilson.

The bearded figure of "Uncle Sam" was drawn and created by Thomas Nast, the same cartoonist who created the Republican's elephant and the Democrat's donkey.