CAPE TOWN, South Africa (AP) — As South Africa's anti-apartheid icon Archbishop Desmond Tutu turns 90, recent racist graffiti on a portrait of the Nobel winner highlights the continuing relevance of his work for equality.

Often hailed as the conscience of South Africa, Tutu was a key campaigner against South Africa's previous brutal system of oppression against the country's Black majority. After South Africa achieved democracy in 1994, he continued to be an outspoken proponent of reconciliation, justice and LBGT rights.

The racial insult sprayed last month on a mural of Tutu in Cape Town is “loathsome and sad,” said Mamphela Ramphele, acting chairwoman of the Desmond and Leah Tutu Trust.

South Africans must continue Tutu's work for racial equality, she told The Associated Press.

“Racism is a curse South Africa must escape,” said Ramphele. “Archbishop Tutu's legacy is huge. He fought against racism and fought for the humanity of us all."

Although frail, Tutu is expected to attend a service on Thursday, his birthday, at St. George’s Cathedral in central Cape Town, where as the country's first Black Anglican archbishop he delivered sermons excoriating apartheid.

He was awarded the Nobel Peace Prize in 1984 for his campaign of nonviolent opposition to South Africa’s system of white minority rule.

After retiring as archbishop in 1996, Tutu was chairman of South Africa's Truth and Reconciliation Commission which investigated human rights abuses during the apartheid era.

Despite the serious nature of his work, Tutu brought an irrepressible humor to his frequent public appearances. Notably, he supported LBGT rights and same-sex marriage.

“I would not worship a God who is homophobic and that is how deeply I feel about this,” he said in 2013. "I would refuse to go to a homophobic heaven. No, I would say ‘Sorry, I would much rather go to the other place.’”

Tutu said he was "as passionate about this campaign (for LGBT rights) as I ever was about apartheid. For me, it is at the same level.”

He withdrew from public life in 2010 and issued statements through his foundation. He has been treated for prostate cancer and was hospitalized several times in 2015 and 2016, and underwent a surgical procedure to address recurring infections from past cancer treatment.

At the church service Thursday, fellow anti-apartheid campaigner Alan Boesak is to speak. There will also be an online seminar about Tutu’s life and values to be addressed by the Dalai Lama; the widow of Nelson Mandela, Graca Machel; former Irish Prime Minister Mary Robinson; and South African governance advocate Thuli Madonsela.

Andrew Meldrum, The Associated Press