Best parks to see it: Masai Mara, Amboseli, Lake Naivasha, Lake Baringo, Tsavo

Hippos are said to cause more human deaths in Africa than any other animal. Their innocent look hides a set of long (more than 1 ft or 50 cm) and razor-sharp lower canines and an aggressive mood that shows if disturbed, specially when their territory is invaded, or at night, when they emerge for grazing. During their nocturnal forages they can walk long distances away from the water. On land they are surprisingly agile and fast.

Hippos are usually seen in large groups, submerged in the water or basking nearby. They live in clans of related females and their calves with a territorial male. At lodges and camps located near streams or lakes it is strongly advised not to walk by the shores at night, since a close encounter with a grazing hippo in the dark may be fatal.
Hippos in Amboseli National Park. J.Y./Kenyalogy.com

The Big Five
Other mammals
Birds
Reptiles