Miljo, who was 81, died in her small flat above the clinic of the Centre for Animal Rehabilitation and Education in the Limpopo bush.

With her at the time of her death was Bobby, the first battered Chacma baboon she rescued and nursed back to health in 1980 after spiriting her away from a national park without a permit.

Bobby also died in the fire, along with two other older baboons who lived in her flat, Pierce said.

The fire started at about 8pm on Friday after volunteers and workers had left the centre, Pierce said.

No one else was injured in the blaze, which consumed the clinic, offices and a house on the property.

The cause of the fire is being investigated.

Miljo no longer ran the day-to-day operations of the centre, which cares for more than 400 baboons, but she was a constant presence and a figurehead.

Born in Germany in 1931, she came to South Africa in the 1950s. In a 2008 article about her in The Washington Post Magazine, Miljo said helping baboons taught her why people behave as they do.

"Chimpanzees can be deceitful, just like humans, but baboons haven't learned that yet," she said at the time. "What you learn from the baboons is the truth about yourself."

Miljo nursed orphaned and injured baboons back to health, then pioneered ways of reintroducing whole troops back into the wild, her centre said.

In 1994, the centre successfully released 10 hand-reared baboons back into the wild.

A year later, 70% had survived and had been integrated back into the wild population, a success few expected because it was thought human-reared baboons would not be able to adjust.

"Everybody's still in shock about this," Pierce said.