Hippos will be hippos.
Clearly, this hippo liked/tolerated his owner about as much as it was possible for a hippo to do so. But there’s a limit on how far you can stretch nurture vs. nature. I think that those built-in limits are pretty clear for hippos and tigers, perhaps less so for pit bulls, but that’s a whole other discussion—which many on this thread will jump into enthusiastically.
Clearly, some animals that we don’t think of being companionable can grow to be somewhat tolerant of people. Lions come to mind... as do a couple of African hyena tamers and owners.
Good points. In Humphrey’s case, he was signaling that a rough patch lay ahead. For example, he treed a grandfather and grandson for two hours. They were canoeing on a river that ran through the owner’s farm. Humphrey came after them, and they managed to make it up a tree before worse came to worst. Took Humphrey’s owner two hours to lure him away with apples, so the pair could escape.
It was just a matter of time.