“Ahmed Kathrada has passed on. Details to follow,” the Kathrada Foundation said just before 6am local time (0400GMT).
Affectionately known as Uncle Kathy, the 87-year-old liberation struggle stalwart was hospitalised in Johannesburg earlier in March after surgery to relieve blood clotting on the brain.
On Monday, the Foundation said his condition had deteriorated rapidly and was “serious” with pneumonia affecting both lungs.
Kathrada, who dedicated his life to fighting the racial injustice of white-minority rule, was also one of the most senior African National Congress (ANC) leaders to criticise President Jacob Zuma’s presidency as allegations of government corruption and maladministration mounted.
Last year, Kathrada wrote an open letter calling on Zuma to resign as a series of scandals, from using taxpayers money to upgrade his rural Nkandla home to summarily firing former finance minister Nhlanhla Nene in 2015, rocked Africa’s most industrialised economy.
“I am not a political analyst, but I am now driven to ask: “Dear Comrade President, don’t you think your continued stay as President will only serve to deepen the crisis of confidence in the government of the country?,” Kathrada said then.
Born to immigrant Indian parents in the small town of Schweizer-Reneke in the North West province just before the Great Depression in 1929, Kathrada became involved in politics at the age of 12 when he distributed leaflets for the Young Communist League of South Africa.
Following decades of activism, Kathrada was sentenced to life imprisonment and hard labour in 1964, together with seven other ANC luminaries such as Mandela, Walter Sisulu and Govan Mbeki, after a guilty verdict during the Rivonia treason trail.
Jailed at the age of 34, Kathrada spent the next 18 years at the maximum security section on apartheid’s most notorious prison, Robben Island, a few miles offshore Cape Town city.
He was moved to Pollsmoor prison in 1982 and was released from jail on 15 October 1989 at the age of 60, having spent just over 26 years in jail for his anti-apartheid activities.