Nobel peace prize winner Desmond Tutu on Sunday celebrated four decades of service as a bishop at a mass at St. Mary's Cathedral and central Johannesburg.

Anglican Archbishop Emeritus Tutu, 84, was dean at St. Mary's when he was appointed bishop of Lesotho 40 years ago. Tutu later became the first black archbishop of Cape Town where he was an outspoken opponent of South Africa's apartheid regime, which enforced a harsh system of racial discrimination. Tutu was awarded the Nobel peace prize in 1984.

Since the end of apartheid in 1994, Tutu has campaigned for human rights, to fight HIV/AIDS, racism, sexism, homophobia and transphobia.