Martin Luther King Jr.
Once, when he was 14, King won a contest with a speech about civil rights.  When he was going back home on a bus, he was forced to give up his seat and stand for the bus ride so a white person could sit down.  At the time, white people were seen as more important than black people.  If a white person wanted a seat, that person could take the seat from any African American.  King later said having to give up his seat made him "the angriest I've ever been in my life."