Which figure is known for refusing to move to the back of the bus, an act that ultimately sparked the civil rights movement?

Rosa Parks is recognized for her courageous act of refusing to give up her seat to a white passenger on a bus in Montgomery, Alabama, in 1955. This defiance was a pivotal moment in the civil rights movement, as it highlighted the injustices of racial segregation and inspired others to take action against such discrimination. Parks' arrest led to the Montgomery Bus Boycott, which lasted for more than a year and was a significant organized effort that aimed to end segregation on public transportation. Her bravery not only led to legal changes but also galvanized support for the broader civil rights struggle, influencing many future activists and the direction of the movement.

The other figures mentioned played crucial roles in civil rights and social justice but in different contexts. Martin Luther King Jr. is known for his leadership and advocacy for nonviolent protest, Malcolm X for his promotion of black empowerment through more militant means, and Frederick Douglass for his work as an abolitionist and advocate for equality in the 19th century.