Uncle Sam was the nickname of the United States, not a president.
"On this day in 1813, the United States gets its nickname, Uncle Sam. The name is linked to Samuel Wilson, a meat packer from Troy, New York, who supplied barrels of beef to the United States Army during the War of 1812. Wilson (1766-1854) stamped the barrels with "U.S." for United States, but soldiers began referring to the grub as "Uncle Sam's." The local newspaper picked up on the story and Uncle Sam eventually gained widespread acceptance as the nickname for the U.S. federal government."