On December 1, 1955, Parks became famous for refusing to obey bus driver James Blake's order that she give up her seat to make room for a white passenger. This action of civil disobedience started the Montgomery Bus Boycott, which is one of the largest movements against racial segregation. In addition, this launched Martin Luther King, Jr., who was involved with the boycott, to prominence in the civil rights movement. She has had a lasting legacy worldwide.
For more information on Rosa Parks check out http://en.wikipedia.org/wiki/Rosa_Parks