The Ahmed Kathrada Foundation has extended its condolences to the family, friends and comrades of Winnie Madikizela-Mandela, who passed away at the age of 81 on Monday.

Madikizela-Mandela, an anti-apartheid struggle hero and former wife of late president Nelson Mandela, dedicated her life to fighting societal injustices.

"It is with sadness that we received the news of Comrade Winnie's passing after a period of illness that saw her in and out of hospital," said the foundation’s executive director, Neeshan Balton.

"We wish her family and friends strength during this trying time and trust that they will bear this difficult period with courage."

Foundation chairperson Derek Hanekom said that Madikizela-Mandela and fellow struggle icon Ahmed Kathrada had had a close relationship.

"Comrade Winnie and Ahmed Kathrada shared a strong sense of camaraderie and friendship that extended from before Kathrada's imprisonment, when he became close to both the Sisulu and Mandela families," he said.

Hanekom also acknowledged the major role that Madikizela-Mandela played during the fight against the apartheid regime.

"For the broader South African public, Comrade Winnie became an iconic symbol against apartheid, and especially so at a time when the African National Congress and other liberation organisations were almost crushed. Her militancy, courage and defiance kept the struggle against apartheid alive."