Ulysses S. Grant was the 18th President of the United States and a prominent Union general during the American Civil War, known for his leadership in key military campaigns. He played a crucial role in securing Union victories, particularly at battles like Vicksburg and Appomattox, which were pivotal in the defeat of the Confederacy. Grant's military strategies and relentless pursuit of Confederate forces helped turn the tide of the war, establishing him as a significant figure in American history.