Final answer:
Thomas Nast, a cartoonist for Harper's Weekly, popularized Uncle Sam and developed other political symbols like the donkey and elephant for the Democratic and Republican parties.
Step-by-step explanation:
The famous political cartoonist who made Uncle Sam popular was Thomas Nast. He was a cartoonist for Harper's Weekly and is often credited with creating the visual representation of Uncle Sam that is commonly recognized today. During the 1860s, Nast developed iconic symbols in American political cartoons, such as using the donkey and the elephant to represent the Democratic and Republican parties, respectively. He was a pivotal figure in the use of allegorical characters to symbolize political entities and social commentary.
Uncle Sam, a personification of the U.S. government, and Columbia, a representation of the American people, were frequent figures in Nast's work. His cartoons often addressed pressing social and political issues of the time, including U.S. neutrality, the spread of imperialism, and the Ku Klux Klan's influence in the 1920s. One prominent example includes the cartoon 'Stranger Things Have Happened' from 1879, showcasing his creatively symbolic style.