The hippopotamus, (hippos meaning "horse" and potamos meaning "river"), often shortened to "hippo", is a large, mostly plant-eating African mammal.

The hippopotamus is semi-aquatic, inhabiting rivers and lakes in sub-Saharan Africa in large groups of up to 40 hippos. During the day they remain cool by staying in the water or mud; reproduction and childbirth both occur in water, where territorial bulls preside over a stretch of river. They emerge at dusk to graze on grass. While hippos rest near each other in territories in the water, grazing is a solitary activity and hippos are not territorial on land.

Despite their physical resemblance to pigs, their closest living relatives are really whales, porpoises and the like. The hippopotamus is recognizable for its barrel-shaped torso, hairless body, stubby legs and tremendous size. It is similar in size to the White Rhinoceros; only elephants are consistently larger and despite its stocky shape and short legs, it can easily outrun a human. Despite its popularity in zoos and cuddly portrayal as gentle giants in fiction, the hippopotamus is among the most dangerous and aggressive of all mammals. Although there are an estimated 125,000 to 150,000 hippos throughout Sub-Saharan Africa, they are still threatened by poaching and habitat loss.