When Jane Goodall, chimpanzee activist and the first scientist to observe that apes as well as humans use tools, "knocks at somebody's door they come," said Ian Redmond, chair of the Ape Alliance, a coalition of conservation groups.

"Jane is known by and trusted by heads of state, the Dalai Lama ... She's become an icon of conservation," said Redmond, who has known Goodall since the 1980s, the point at which she went from being a scientist to being an activist.

Indefatigable at 78, Goodall criss-crosses the planet pleading the cause of chimpanzees -- the apes she came to Africa to study more than half a century ago in what is now Tanzania -- then still a British protectorate called Tanganyika.

Slim, looking younger than her years and with long grey hair tied back from the face, Goodall speaks with quiet composure, sufficiently sure of her own influence not to need to charm her listeners.

"She treats the audience to very accurate renditions of a chimpanzee at the start of every conference," Redmond told AFP.

A recent visit to Nairobi was no exception with Goodall regaling the assembled company with a whole variety of chimp sounds.

A committed vegetarian, Goodall now spends just a few weeks a year in the Gombe Stream National Park in Tanzania where she cut her teeth as a scientist -- the first researcher to live year-in year-out in the bush with the apes she was studying.

It was Louis Leakey, the famed paleontologist, whom Goodall met whilst visiting friends in Kenya, who suggested she go study chimpanzees, reckoning correctly that she had the right temperament for lone research in the bush.

Born two years after the American Dian Fossey, who devoted her life to the study of the mountain gorilla in neighbouring DR Congo and Rwanda, Goodall started out in an age when it was unthinkable for a nice young lady to go off into the bush without a chaperone.

Her mother Vanne came along and, according to Goodall, spent the better part of the day at the camp they had set up, with only the ladies' Tanzanian cook -- whom Goodall remembers chiefly for his taste for local banana wine -- for company.

Goodall recounts how, in the evenings when she gave way to despondency, feeling she was getting nowhere with her research, Vanne would encourage her, pointing out what she had accomplished.

It was in the Gombe park that Goodall famously witnessed a chimpanzee she had named David Greybeard using a grass stalk to get termites out of a termite mound.

She later saw Greybeard and a second animal called Goliath stripping leaves off a twig to turn it into a better tool for digging out termites.

Until her discovery scientists had thought that using tools was one of the defining characteristics of humans.

Leakey packed Goodall -- who had no first degree, only secretarial training, off to Darwin College at Cambridge university for doctoral research.

She became only the eighth person to earn a PhD at Cambridge without possessing a first degree.

In 1964 Goodall, who has authored a number of books, married Dutch photographer Hugo van Lawick, who had immortalised her and her chimps in National Geographic and LIFE. A model of David Greybeard graced the wedding cake.

The couple has a son Hugo Eric Louis Van Lawick, named, biographer Meg Greene says, not only after his father but also after Goodall's uncle Eric and her mentor Louis Leakey.

The boy was nicknamed Grub, and Goodall relied on some of her observations about apes in raising him.

"The chimpanzees have an extremely close bond between mother and child," she explains. "The mother is constantly with the child, and I raised Grub this way. I never left him for a full day until he was 3 years old."

Her second husband Derek Bryceson, the director of Tanzanian national parks came into her life in 1973. He and Goodall fell in love, divorced their respective partners and married in 1975. Five years later Bryceson died.

It was in the decade following his death that Goodall made the move into advocacy.

"She's a scientist but also someone able to influence decision makers. She uses this influence to try to combat the continuing loss of primate habitats the world over," Redmond said.

"Jane has successfully gone from raising awareness of chimps, the argument being that they are interesting because they are like us, to making people think about the biocentric view."