The revolutionary leader who played a crucial role in the American Civil War as a general was Ulysses S. Grant. As the commanding general of the Union Army, Grant's military strategies and determination were pivotal in defeating the Confederate forces. His leadership during crucial battles, including the Siege of Vicksburg and the Battle of Gettysburg, significantly contributed to the Union's victory. Post-war, Grant served as the 18th President of the United States, advocating for Reconstruction and civil rights for freed slaves.