A 41-year-old South African man, Marius Els, was found dead in a river running through his farm over the weekend. He had been mauled and left submerged by his 2,645-pound pet hippopotamus, Humphrey. Here, a guide to this strange, horrifying tragedy:

Who keeps a hippo as a pet?
If Els' story is any guide, you have to have an extraordinary love of wild animals. Els, an army major and part-time farmer, also kept a giraffe and a rhino on his 400-acre property along the Vaal River. Els bought the hippo when it was 5 months old, after it grew too big for people who rescued Humphrey from a flood. Els said Humphrey, now 6 years old, became "like a son" to him. Els used to ride on Humphrey's back, feed him by hand, and even brush his teeth. (Watch a video below of Els showing off his pet hippo.)

Didn't he know that was dangerous?
He probably should have. Hippos are "said to kill more people each year than lions, elephants, leopards, buffalo, and rhinos combined," says David Smith in Britain's Guardian. They have giant canine teeth, and can run as fast as 30 miles per hour even though they weigh up to three tons. Els knew all that, but he was convinced that Humphrey was "loveable" and a "gentle giant." "It's a little bit dangerous, but you get used to it, and I trust him with my heart that he will not harm anybody," Els said earlier this year. People "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."

Were there any warning signs?
Yes. In August, the hippo was blamed for killing livestock belonging to Els' business partner. Humphrey also occasionally broke out of its enclosure and chased golfers at a nearby club. And in March, Humphrey chased a 52-year-old man and his grandson who had been canoeing in the river. They climbed up a tree and had to stay there, terrified, until Els arrived to coax Humphrey away with an apple so paramedics could rescue the men. Friends told Els he was tempting fate because Humphrey was still a wild animal and could not be tamed. "We tried to warn him," a neighbor told a local newspaper, "but he wouldn't listen."

Sources: Daily Mail, GlobalPost, Guardian, Sky News

Watch a video of Els riding Humphrey: