The 20th-century leader in South Africa known for his role in anti-apartheid activism was Nelson Mandela. He became a prominent figure in the struggle against the oppressive apartheid regime, advocating for equality and justice for all South Africans. Mandela's activism led to his imprisonment for 27 years, during which time he became a symbol of resistance against racial segregation. Upon his release in 1990, he played a crucial role in negotiating the end of apartheid, ultimately becoming South Africa's first black president in 1994, showcasing the power of reconciliation and unity.