Final answer:
Malcolm X was the most visible spokesman for the Nation of Islam in the 1960s, known for his eloquent speeches and radical views on black separatism. After leaving the NOI and converting to mainstream Islam, he began advocating for racial cooperation and was assassinated in 1965.
Step-by-step explanation:
The most visible spokesman for the Nation of Islam during the 1960s was Malcolm X, originally born Malcolm Little. Malcolm X was renowned for his charisma as a speaker and for openly preaching about the separatism and self-sufficiency of black Americans. His radical views and exceptional oratory skills rapidly propelled him within the organization's hierarchy, making him an influential figure in the civil rights movement.
After a period of deep involvement with the Nation of Islam, Malcolm X grew critical of its leader Elijah Muhammad and left the organization in March 1964. He subsequently formed the Muslim Mosque, Inc., and his journey to Mecca led to a significant change in his outlook regarding race and cooperation between different ethnic groups. He adopted more inclusive philosophies and came up with the slogan 'Ballots or bullets', advocating a non-violent approach unless forced otherwise. Unfortunately, his newly formed views and departure from the NOI likely contributed to his assassination by members of the NOI in 1965.