A farmer in South Africa has been killed by his pet hippopotamus, after repeated warnings that it was a wild animal that could never be tamed.

Marius Els, 40, an army major, was bitten to death by the 1.2 tonne hippo he christened Humphrey and tried to domesticate on a farm in Free State province.

Els's savaged body was found submerged in the river where, years earlier, the hippo had been rescued from a flood. It grew too big for the people who adopted it and was bought by Els at the age of five months, becoming a pet on his 400-acre farm and learning to swim with humans.

Earlier this year, Els was photographed riding on the five-year-old hippo's back. "Humphrey's like a son to me, he's just like a human," he said. "There's a relationship between me and Humphrey and that's what some people don't understand.

"They think you can only have a relationship with dogs, cats and domestic animals. But I have a relationship with the most dangerous animal in Africa."

But Els's wife, Louise, a pharmacist, expressed misgivings, and the hippo had caused trouble before. South African media reported earlier this year that a 52-year-old man and his seven-year-old grandson spent two hours in a tree after being chased by Humphrey while canoeing on the river that passes through the farm. Els finally tempted the hippo away with an apple while the pair were rescued by paramedics.

Humphrey was also blamed for killing calves belonging to Els's business partner. The animal also frequently broke out of its enclosure and chased golfers at a local golf club.

Els, who also kept giraffe and rhino, claimed the sound of his voice would lure Humphrey back home. He regarded the hippo as "loveable" and a "gentle giant".

Armed with giant canine teeth, hippos are said to kill more people each year than lions, elephants, leopards, buffalo and rhinos combined. They can move at speeds of up to 30mph despite weighing up to three tonnes.