Winnie Madikizela-Mandela, a leading figure in South Africa’s anti-apartheid movement, died today (April 2) at age 81.

Per Reuters, family spokesperson Victor Dlamini announced that Madikizela-Mandela—who many called “Mother of the Nation”—died surrounded by family members at a hospital in Johannesburg, South Africa, after a long, undisclosed illness.

Born in 1936, Madikizela-Mandela became politicized at an early age by working as a hospital social worker, as reported by Reuters. She moved to Johannesburg in 1953 to study social work, where she met and married anti-apartheid revolutionary Nelson Mandela

When Mandela was sentenced to life in prison for treason, Madikizela-Mandela led a 27-year campaign for her husband’s release, becoming a prominent figure in the campaign against racism and apartheid. South Africa’s government frequently harassed Madikizela-Mandela for her activism, placing her in solitary confinement, putting her under house arrest and banishing her to a remote town where she was under constant surveillance.

NPR reports that, in a 2004 interview with Tavis Smiley, Madikizela-Mandela said:

I probably would have never turned out to be what I am today had it not been the viciousness of apartheid. No human being with any honor and pride could have stood by and be a spectator and witnessed the horrors of apartheid without protesting. You had to fight for your dignity.

During her later years, Madikizela-Mandela served as a member of South Africa’s Parliament and advocated for immigrants who came under attack during xenophobic riots, The Gaurdian reports.

Learn more about Madikizela-Mandela’s life and legacy in the 2017 documentary “Winnie,” which is currently available on Netflix.