By Roxanne Khamsi

Primate research has yielded a number of celebrity chimps. They have gained fame and sparked debates by doing everything from signing words to orbiting our planet. The following common chimpanzees (Pan troglodytes) have left their mark on history, and given us insight into their species and our own.

Sultan
The famous psychologist Wolfgang Kohler gained considerable understanding of tool use in chimps during the early twentieth century by studying the behaviour of individuals such as Sultan. Kohler would hang bananas from a ceiling and watch Sultan position boxes and sticks to knock the food down.

Flo
Flo was one of the first female chimpanzees to enter Jane Goodall's camp in Tanzania's Gombe National Park in 1961. The chimp had such great sex appeal that her male suitors followed her there. Her mothering techniques and social behaviour taught researchers a tremendous amount about the way chimpanzees interact with their offspring.

Washoe
Born in the mid-1960s in Africa, Washoe was brought to the United States by the Air Force. Allen and Beatrix Gardner adopted her for their research. The couple raised her in their home as if she was a human child and taught her to speak American Sign Language.

As a result, Washoe has been called the first non-human to acquire language. She and three other younger chimps raised in the house learned to do chores just as human children do. For example, they would help to clear the table after dinner and ask to be excused to use the toilet. Their rearing gave researchers the ability to compare chimpanzee development directly with that of humans.

Ham
On 31 January 1961, Ham blasted off from Cape Canaveral into space. He was trained as part of an experiment to reassure experts that a human could endure the trip. After travelling 680 kilometres in a Mercury capsule, he splashed down safely in the Atlantic Ocean.

Enos
In November 1961, Enos trumped his fellow chimp Ham by doing two orbits of the Earth in a spacecraft. His trip served as a full dress rehearsal for the flight that carried US astronaut John Glenn into orbit.

Nim Chimpsky
Named in tribute to the language theorist Noam Chomsky, Nim was taught to sign words. Although he could use basic signs, it was generally agreed that he did not develop complex language skills. After being sold to a medical lab to be the subject of experiments, Nim was pulled out by activists and placed in a wildlife sanctuary. He died in March 2000 of a heart attack.

Oliver
Oliver, a chimp with a peculiar look, gained fame as the 'missing link' in the story of human evolution. According to reports, he liked to walk around on his hind legs and sit cross-legged on chairs. Oliver also had a strange morphology, including an unusually bald and round cranium, and a less prominent jaw than his fellow chimps. These gave him a more humanoid appearance.

In the 1970s, scientists reported that his cells contained only 47 chromosomes: one more than humans and one fewer than chimpanzees. There was much speculation about whether Oliver represented a new species of chimp, or a hybrid. But research in the past decade has shown that he actually had the 48 chromosomes expected for chimpanzees.

Ai
Born in the mid-1970s, Ai has impressed scientists with her ability to deal with number puzzles. At a research centre in Japan, she has shown an unusual aptitude for remembering numerical sequences and working with computers. The Japanese team studying her also claims that she has the ability to understand the concept of zero, which is considered part of a fairly sophisticated sense of maths. 'Ai' is the Japanese word for love.

Frodo
Until 2002, Frodo was simply a dominant alpha male living in Gombe National Park. In that year, however, he caused consternation by killing the 14-month old baby girl of a local park worker. Chimpanzees normally hunt other mammals, such as colobus monkeys, but Frodo had attacked people before. Park officials considered killing Frodo, but researchers decided that the animal's actions, when taken in context, did not warrant this. Frodo later suffered an undiagnosed ailment that has contributed to a loss of status among his fellow chimps.

Clint
Scientists mapping the chimpanzee genome used DNA from Clint. The chimp died unexpectedly, aged only 24. Researchers decided to preserve some of his cells for future research.