Helen Bamber, who at 19 traveled alone to post-World War II Germany to care for former inmates of the Bergen-Belsen concentration camp and became one of the world’s most relentless advocates for the victims of war, genocide and torture, died Aug. 21 in London. She was 89.

Her death, after a series of strokes last year, was announced by the Helen Bamber Foundation.

Started in 2005, the British organization expanded on the rehabilitative work Ms. Bamber began 20 years earlier with the Medical Foundation for the Care of Victims of Torture, a London-based group that provides counseling and documents torture cases to support asylum claims.

The organizations have been credited with helping thousands of victims — of state-sponsored terror, human trafficking and gang violence — adjust to life after physical and psychological trauma. A psychotherapist of “fierce gentility,” in her biographer’s words, Ms. Bamber treated clients from Bosnia, Chile, Congo, Iran, Rwanda, Sri Lanka — as well as British World War II veterans whose post-traumatic stress was little understood by the medical establishment for decades.

Ms. Bamber, whose parents were Jewish, grew up in London in a home where the Nazi threat was drummed into her relentlessly; at bedtime, her father read her passages of Hitler’s anti-Semitic tract “Mein Kampf.”

In 2009, British human rights organizer Helen Bamber stands in front of art installation "Journey," which depicts the world of human trafficking. (STAN HONDA/AFP/Getty Images)

After the war, she joined the Jewish Relief Unit, a group of health and other professionals who went to Germany to help Holocaust survivors.

Dispatched to Bergen-Belsen, she helped distribute food and blankets to 12,000 former camp internees who had been transferred to old army barracks. They were emaciated and dying of typhus.

“People wanted to tell their story and I was able to receive it,” she once told the Observer, a British publication. “They would hold me and dig their fingers in and rasp this story out. . . . They would rock back and forth, and I would say to them, ‘I will tell your story. Your story will not die.’ It took me a long time to realize that that was all I could do.”

Most horrifying to Ms. Bamber was the shift in sentiment toward the camp survivors by those there to help and protect them. They were initially viewed as examples of human resilience amid unspeakable atrocities but, as the years passed, many remained displaced persons without hope of resettlement.

The authorities came to view the displaced people with contempt. “And that I found very frightening as a young person, watching those attitudes change,” Ms. Bamber said, according to the Daily Telegraph.

The 18 months she spent in Germany would define the rest of her life. She concluded that the world was made of two kinds of people: the bystanders and the witnesses. “I just couldn’t remain a bystander,” she said.

As an Amnesty International volunteer in the 1970s, Ms. Bamber had been involved in the human rights group’s high-profile “campaign against torture.” But Amnesty was mainly focused on documenting abuses, rather than treating victims. Ms. Bamber’s medical foundation, which was renamed Freedom From Torture in 2011, was among several groups that began to fill the void.

Malcolm Smart, a longtime official with Amnesty International and Human Rights Watch who succeeded Ms. Bamber at the helm of the medical foundation in 2002, called her “definitely one of the drivers of the greater appreciation of torture as a crime and the need to address it.”

“She talked to people who had been through those traumatic situations, documented it and brought it to the attention of policymakers, who were often not aware of the details,” Smart said. He added that Ms. Bamber was adept at fundraising in the film and theater community.

“I marvelled that anyone could find the strength to engage with so many desperate stories without being engulfed by them,” actor Colin Firth told a British interviewer. Ms. Bamber advised Firth on his starring role in “The Railway Man,” a 2013 movie based on the life of British soldier Eric Lomax, who endured torture and forced labor by the Japanese during World War II.

Lomax, who died in 2012, became a client of the medical foundation in the late 1980s and once called Ms. Bamber a pivotal figure in his rehabilitation late in life.

“My first meeting with her was like walking through a door into an unexplored world, of caring and special understanding,” he said. “She learned in Belsen the importance of allowing people to tell what had been done to them, the power of listening to their testimony and of giving people the recognition that their experience deserves.”

Helen Balmuth was born May 1, 1925, in London. From a young age, she was forced to act as conciliator between her quarrelsome parents, whose marriage had been arranged.

In a home where plates were thrown and furniture was thrashed in anger, Helen grew up a sickly, bedridden child who dreamed of escaping from home. She soon joined the Jewish Relief Unit.

“I felt I had to face something, the fear in myself,” she told the Guardian in 2000. “I had to understand other people’s fear, and I had to understand something about overcoming fear living. How does one live with the knowledge of atrocity?”

Upon her return to England in 1947, she was appointed to the Committee for the Care of Children from Concentration Camps and oversaw more than 700 orphaned children. She recalled to her biographer, Neil Belton, “their stony little faces, giving nothing back, their skeptical eyes — a complete lack of trust as though to say, ‘What are you going to do for me, how can I negotiate with this person for what I want?’ ”

In trying to help them adjust to society through work or school, she said she confronted a woeful ignorance about the young survivors.

In Belton’s 1998 biography, “The Good Listener,” Ms. Bamber remembered a promising young refu­gee who was applying to an elite school. He was clearly deficient in some subjects. One school official sniffed, “Didn’t they give them any books to read in those camps?”

Soon after her return from Bergen-Belsen, she married Rudi Bamberger, a German Jewish refugee who later anglicized his surname to Bamber. He had seen his father beaten to death by Nazi thugs, and his mother died in a concentration camp.

He grew increasingly walled off from her and fell into a severe depression that helped end the marriage, Ms. Bamber said. Survivors include their two sons and a granddaughter.

Starting in the 1950s, Ms. Bamber began working as a personal assistant and editor to doctors. She helped the renowned physician and medical ethicist Maurice Pappworth with his archive of medical abuses on human patients. “He was as preoccupied as I was with this question of total power, total helplessness,” she told the Guardian.

Ms. Bamber joined Amnesty International soon after it was formed in 1961. In a senior voluntary capacity, she chaired the medical group in the British section and helped specialists interview and examine asylum-seekers who claimed to be victims of state-sponsored torture.

In the 1970s, she was particularly active in cases involving the Pinochet regime in Chile and the military junta in Argentina, both of which tortured, killed or “disappeared” thousands of perceived opponents.

She left Amnesty in 1985 to start the Medical Foundation for the Care of the Victims of Torture, which saw 45 clients in its first year — a number that quickly climbed to 2,000. The staff grew to include dozens of doctors, physiotherapists, reflexologists, psychologists, interpreters, aromatherapists and osteopaths.

In addition to partnering with relief agencies such as Oxfam, the medical foundation provides reports to medical journals and United Nations agencies. The documentation aspect of her work was critical, she said, because no country ever admits to torture.

At Bergen-Belsen, Ms. Bamber often said, the stench of death was like the dank, overripe scent of crushed geraniums. More than 50 years later, she grew geraniums at her home in London — a reminder of man’s potential for inflicting pain on fellow man.

“If we look at the world today,” she told the Times of London in 1995, “humanity seems to have learnt very little.”