Chimpanzees are supposed to be the “good” apes, cute and funny, the hairy little people depicted in thousands of films and TV shows. But recent news out of western Africa shows they can be brutally fierce.

A chimp attacked and killed a Sierra Leone man who was driving Americans to a wildlife refuge Sunday. Another man lost part of his hand in the attack.

Some news reports said a group of up to 20 chimps that had broken out of their enclosures gang-attacked the men, while other stories have pinned responsibility on one animal, possibly a chimp named Bruno, the undisputed alpha male of the Tacugama Chimpanzee Sanctuary. The powerful ape reportedly punched out a window of the taxicab the men were in and assaulted the driver, Issu Kanu, before attacking the passengers.

“This thing was on a rampage, and it acted like it wanted to kill every one of us,” Gary Brown, one of the Americans in the cab, told an Austin, Texas, TV station. “And it had hatred in its eyes.”

Hardly the behavior we would expect from Tarzan’s little pal Cheetah. But such attacks are not unprecedented.

BBC Wildlife magazine reported in 2004 that chimp attacks on people in Uganda had increased, with 15 children either mauled or killed in the past seven years.

Chimps certainly have the strength. An adult male chimpanzee may be only 4 feet tall and weigh 110 pounds, but he is at least five times as strong as a man.

That chimps can be homicidal should not be surprising. Biologically, they are the closest animals to humans, sharing more than 98 percent of the same DNA with our far more deadly species.

Still, attacks on humans remain rare, and the cause of the Sierra Leone incident is unknown. It’s possible, chimp expert Anne Pusey said that Bruno and his mates were displaying territorial aggression. Male chimps patrol their territory in bands and will sometimes kill males from neighboring groups. Typically, a few animals will hold a lone victim down while the others beat and tear at it.

“This attack seems quite a lot like what they sometimes do to each other,” said Pusey, professor of ecology, evolution and behavior at the University of Minnesota.