Orcas were named killer whales by ancient sailors, who observed pods of the mammal hunting down prey and taking out larger whales at sea. They were often called "whale killer," which eventually became "killer whale." However, the orca is not a whale at all, but is actually part of the dolphin family, Delphinidae. They are the only species in their specific genus, but are most closely related to dolphins from Australia and South East Asia.