The civil rights activist best known for her role in the Montgomery Bus Boycott is Rosa Parks. On December 1, 1955, Parks famously refused to give up her bus seat to a white passenger, igniting a pivotal protest against segregation in public transportation. Her act of defiance became a symbol of the struggle for racial equality in the United States. Parks' courageous actions contributed to the success of the boycott, leading to a Supreme Court ruling that declared segregation on public buses unconstitutional.