The sperm whale is the largest odontocete, or toothed whale. It has been portrayed frequently in art and literature as a symbol of the great whales, and is best known as the leviathan Moby Dick in Melville's novel by that name. Unique in appearance, the sperm whale seems to have social characteristics that, to date, also appear to be unique among whales. Sperm whales are among the deepest diving cetaceans, and are found in all oceans of the world. Females and their young travel in permanent units, whereas the much larger males rove between breeding and feeding grounds, as well as among groups of females when breeding.

The head of the sperm whale is blunt and squared off, and has a small, underslung jaw. The head is also large, and makes up to 1/3 the total body length and more than 1/3 of its mass. A single blowhole is located forward on the left side of the head, and the blow, which is bushy, is projected forward rather than straight up as it is with other whales. Its body has a wrinkled, shriveled appearance, particularly behind the head.

The sperm whale is usually a dark, brownish gray with light streaks, spots and scratches. The skin around its mouth, particularly near the corners, is white. The ventral (underside) of the body is a lighter gray and may have white patches.

The sperm whale has a squat dorsal fin, followed by knuckles along the spine. Its flippers are small and slightly tapered, while its flukes are broad, measuring as much as 16 feet (5 m) from tip to tip.

Adult males reach lengths of 49-59 feet (15-18 m) and weigh up to 35-45 tons (31,750-40,800 kgs). Adult females are much smaller, growing to about 36 feet (11 m) and a maximum weight of 13-14 tons (12,000-12,700 kg)