Final answer:
Reverend Martin Luther King Jr. was a prominent activist against the Jim Crow laws. He organized protests and demonstrations, including the Montgomery Bus boycott, to fight for the rights of African Americans.
Step-by-step explanation:
The prominent activist against the Jim Crow laws was Reverend Martin Luther King Jr. He, along with the Southern Christian Leadership Conference (SCLC), organized protests and demonstrations in the southern part of the United States. They advocated for nonviolence and conducted sit-ins at lunch counters and marches to protest the unfair treatment of African Americans.
A major success of their activism was the Montgomery Bus boycott, where Rosa Parks was arrested for refusing to give up her seat to a white person. This protest lasted for over a year and ultimately led to a Supreme Court ruling that declared racially segregated seating on buses unconstitutional.