Denis Goldberg, one of two surviving political activists convicted in the so-called Rivonia Trial, which put Nelson Mandela and seven others in prison for many years and proved a turning-point in South Africa’s long struggle against apartheid, died on April 29 in Cape Town. He was 87.

His family, in confirming the death, said he had been treated for lung cancer.

Mr. Goldberg’s career, first in the armed resistance movement and later in the post-apartheid era, encapsulated much of his country’s modern history, from the racial nuances of the struggle against white minority rule to the reluctant acknowledgment of — and disillusion with — the corruption that became a byword in early 21st-century South Africa.

At the trial, which lasted from 1963 to 1964, many of those accused of sabotage were expecting the death sentence. Indeed, in a celebrated address from the dock, Mr. Mandela said his ideal of a democratic and free South Africa was, “if needs be, an ideal for which I am prepared to die.”

When Judge Quartus de Wet pronounced life sentences on eight defendants, Mr. Goldberg’s mother, Annie Goldberg, who was in the public gallery, did not hear what he said.

“Denis, what is it?” she called out. “What did the judge say?”

Mr. Goldberg replied: “Life! Life is wonderful!”