The man known affectionately as "Uncle Kathy" is no more.

Ahmed Kathrada, anti-apartheid activist, politician, and community leader best known for his close relationship with former South African president Nelson Mandela, passed away in Johannesburg in the early hours of Tuesday.

The 87-year-old, who spent 26 years as a political prisoner on Robben Island and then Pollsmore prison, struggled with a brief illness following brain surgery, his foundation said.

READ MORE: Anti-apartheid icon Ahmed Kathrada dies

South African leaders across the political spectrum rallied behind his legacy, and paid tribute to the anti-apartheid icon known for his fierce opposition to racism and steadfast commitment to social justice.

Despite being eligible for state burial as one the country's foremost anti-apartheid icons, the foundation said Kathrada had requested a simple burial as per Islamic tradition.

Ari Sitas, head of school at the Department of Sociology at the University of Cape Town, said humility was Kathrada's trademark.

"He was emblematic of that generation of leadership in the ANC - a generation that sacrificed everything, came out humble, came out proud and without hatred. I am highly respectful of him and the role he played.

"He was the consistent moralist; humble and fearless," Sitas told Al Jazeera.

History of activism

Born in 1929, Kathrada became involved in politics at an early age, enduring a series of arrests as a young activist.

In 1952, he was sentenced to nine months imprisonment with Mandela for organising the Defiance Campaign, considered one of the first large-scale political mobilisations against apartheid laws. In 1956, he was put on trial for high treason, again with Mandela and Walter Sisulu. They were subsequently acquitted.

He was aware that problems could exist during a transition period [but] moral integrity had to win out in his imagination.

Ari Sitas, University of Cape Town

In 1963, Kathrada was arrested at Liliesleaf farm, an ANC safe house in Rivonia, and was accused of attempting to overthrow the government. In 1964, he was found guilty along with 10 other ANC members as part of the now-infamous Rivonia trial and was sentenced to life imprisonment.

He was released from prison in 1989 and served on the ANC committee, eventually elected as a member of parliament following South Africa's first democratic elections in 1994

Between 1997-2006, he was chairperson of the Robben Island Museum Council. The following year, he launched the Ahmed Kathrada Foundation focusing on deepening his life-long mission of fighting racism and building a more socially cohesive South Africa

Neeshan Balton, executive director of the Ahmed Kathrada Foundation, said it was a " great loss to the ANC, the broader liberation movement and South Africa as a whole".

"Internationally, he was staunch in his support for the Palestinian struggle. Kathy was an inspiration to millions in different parts of the world," said Balton.

Kathrada remained a close confidant of Mandela until his passing in 2013, an event that Kathrada said left him "bereft and lonely".

On Tuesday, it was the Mandela family who spoke of Kathrada's death as a tremendous loss to their family. His daughter, Zenani Mandela, speaking at the Nelson Mandela Foundation, cried as she described Kathrada as "her second father". 

Despite retiring from government in 1997, Kathrada was still seen as a flag bearer of the larger project of a more equitable country. 

Ayanda Kota, or ganiser for the Unemployed People's Movement, s aid Kathrada's death "comes at a time when the vultures are fighting viciously over the country's resources".

But it was his ability "to step out in his old age and speak against corruption" that made him "a towering figure" who was true to his "generational mission", Mbuyiseni Ndlozi, spokesperson for the Economic Freedom Fighters political party (EFF), said.

"It's important to remember that he never felt entitled," Ndlozi told Al Jazeera.

Following a series of corruption scandals in government, and rising discontent with President Jacob Zuma's administration, Kathrada wrote an open letter to Zuma asking him to step down.

"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?" he wrote.

It was his ability to put moral integrity at the top of his agenda that drew people to Kathrada. 

"He was aware that problems could exist during a transition period [but] moral integrity had to win out in his imagination," Sitas said. "He showed that there were people in the movement who could still put that first."

Section 27, the public interest law centre based in Johannesburg, said in its tribute to Kathrada that it was "this gentle resolve that distinguished this freedom fighter". 

Winner among youth

Kathrada was an extremely popular figure among young South Africans.

Yazeed Kamaldien, a Cape-Town based journalist who accompanied Kathrada to Robben Island a number of times, said his popularity stemmed from a genuine attempt to engage and listen to everyone.

"He never asserted his ego. You never felt that he was trying to impose his experience or knowledge," Kamaldien said.

In an interview in 2015, Kathrada said after more 300 trips to Robben Island since his release from prison - in which he conducted guided tours for global leaders, including former US President Barack Obama and celebrities like pop star Beyonce - he chose to highlight taking a 13-year-old Afrikaner girl suffering from leukemia as his most memorable excursion back.

"It was precisely because she was a child whose dying wish was to visit Robben Island and meet Madiba [Nelson Mandela] that stood out for me," Kathrada said at the time.

Kathrada was also a source of support to the Fees Must Fall (FMF) movement that began in 2015 across South African universities, calling for the end of tuition fees and better access to higher education. 

"Every time we lose someone like this, it's like we lose another guide. It feels as if another light has gone off," Kamaldien said.

Source: Al Jazeera News