The prominent advocate for civil rights who worked alongside Martin Luther King Jr. is Rosa Parks. Known for her pivotal role in the Montgomery Bus Boycott, Parks' refusal to give up her bus seat sparked a significant movement against racial segregation. Her courage became a symbol of the fight for racial equality in the United States. Parks collaborated closely with King and other leaders of the Civil Rights Movement, contributing to organized protests and fostering grassroots activism, which eventually addressed systemic injustices.