Kathrada, a life-long leading activist in the fight against apartheid, died in a Johannesburg hospital on Tuesday. He had been admitted to the hospital earlier in March due to blood clotting on his brain.

After tweeting about Kathrada's deteriorating condition on Monday, the Ahmed Kathrada Foundation announced the activist's death on Twitter around 6 a.m. local time (0400 UTC).

"This is great loss to the ANC, the broader liberation movement and South Africa as a whole," head of the Ahmed Kathrada Foundation Neeshan Balton said in a statement. "'Kathy was an inspiration to millions in different parts of the world."

Affectionately called "Uncle Kathy" by his supporters, Kathrada dedicated a large portion of his life to fighting the system of institutionalized segregation in South Africa that lasted from 1948 to 1991. He spent over 26 years of his life in prison, many alongside his fellow activist Mandela on Robben Island.

"Comrade Kathy was a gentle, humane and humble soul," said Derek Hanekom, a former fellow activist and the current Tourism Minister."He was a determined revolutionary who gave his entire life to the liberation struggle in our country."

Life-long activism, behind and beyond bars

Kathrada was born to Indian immigrant parents on August 21, 1929, in a small town in South Africa's northwestern Schweizer-Reneke province.

Politically activity from his early teenage years, Kathrada was arrested at age 17 after participating in a passive resistance activites that opposed discrimination against Indian South Africans.

After the ANC was banned 1960, Kathrada became a member of party's underground armed wing, Umkhonto we Sizwe ("The Spear of the Nation"). Police arrested him again in July 1963 during a raid on a secret activist reunion at Liliesleaf Farm in Rivonia. After the famous Rivonia trial, Kathranda was sentenced alongside eight others, including Mandela, to life imprisonment and hard labor on Robben Island.

While in prison, Kathrada earned four university degrees.

The ban against the ANC was lifted shortly after Kathrada's release from prison on October 15, 1989, at age 60.

Following the end of apartheid, Kathrada served as a parliamentary counselor from 1994 to 1999 in the first ANC government headed by President Mandela. In 1997, he also became the chairperson of the Robben Island Museum Council, a role he held until 2006.

In the years preceding his death, Kathrada became a vocal critic of President Jacob Zuma and his ANC government,publishing a letter in April 2016 that called for the scandal-ridden president to resign.

cmb/rc (AFP, AP)