The sperm whale (Physeter macrocephalus) is the largest of the toothed whales. It is the only living member of genus Physeter, and one of three extant species in the sperm whale family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia. Its name derives from a waxy liquid called "spermaceti", found in its enormous head. The sperm whale is also known as the cachalot.

Mature males average at 16 metres (52 ft) in length but can reach 20.5 metres (67 ft), with the head representing up to one-third of the animal's length. The sperm whale feeds primarily on giant and colossal squid. Plunging to 3 kilometres (9,800 ft) for prey, it is the deepest diving mammal. Its clicking vocalization, a form of echolocation and communication, can be as loud as 230 decibels underwater, making it the loudest sound produced by any animal. It has the largest brain of any animal on Earth, more than five times heavier than a human's.

The sperm whale is cosmopolitan, living across the oceans in small groups called pods. Units of females and their young live separately from sexually mature males. The females cooperate to protect and nurse their young. Females give birth every four to twenty years, and care for the calves for more than a decade. Living up to 70 years, a mature sperm whale has few natural predators. Calves and weakened adults are taken by pods of orcas.