The famous civil rights activist known for her role in the Montgomery Bus Boycott is Rosa Parks. On December 1, 1955, she refused to give up her bus seat to a white passenger, defying segregation laws. Her arrest sparked the boycott, which lasted over a year, led by Martin Luther King Jr.. The boycott culminated in a Supreme Court ruling that declared segregation on public buses unconstitutional, making Parks a pivotal figure in the civil rights movement.