Conservationist Dame Jane Goodall, a world-leading expert on chimpanzees, has died aged 91.
Her observations helped to reveal how closely related humans are to chimpanzees. She also worked tirelessly for conservation projects around the world.
Dr Goodall died of natural causes while in California on a speaking tour of the US, according to a statement from the Jane Goodall Institute.
It said her discoveries "revolutionised science" and that she was "a tireless advocate for the protection and restoration of our natural world".
The United Nations said it mourned the loss of Dr Goodall, saying that she "worked tirelessly for our planet and all its inhabitants, leaving an extraordinary legacy for humanity and nature".
Greenpeace said it was "heartbroken" by her death, calling her "one of the true conservation giants of our time".
Its co-executive director in the UK, Will McCallum, said: "Dr Goodall's legacy is not only in science but in the global movement she helped spark to protect nature and give hope for a better world."
Dame Jane Goodall revolutionised our understanding of our closest primate cousins
Naturalist Chris Packham told the BBC that he counted her among his heroes, calling her "revolutionary" and "remarkable".
"To have lost a hero at a time when we need all of them on the frontline fighting for life on earth is a tragedy."
