Hiram Rhodes Revel is a significant politician in American history because he was the first African-American ever elected to the United States Congress. During the era of Reconstruction (the roughly 12 years after the Civil War) African-Americans began to gain political rights that had been restricted to them for a century. One of these privileges included running for office.
This is when Revel won a Senator senate, representing the state of Mississippi in 1870 and 1871.