Many believe monk seals got their name from their monk-like preference for solitude; others think that the loose skin around the seals' neck resembles the hood of a monk's robe. Ancient Hawaiians apparently thought neither and named the seal Ilio-holo-i-ka-uaua, which means "dog that runs in rough waters". Monk seals are also sometimes referred to as "living fossils" because as the oldest living members of the pinniped order they have remained virtually unchanged for 15 million years. The population of the Hawaiian monk seal is currently estimated to be between 1,500 and 1,200 individuals. They are considered an endangered species.

Hawaiian monk seals breed in the remote Northwestern Hawaiian Islands, that portion of the Hawaiian island chain which stretches some 1,200 miles northwest from Honolulu to Kure Atoll. These remote islands and atolls, mostly uninhabited by humans, seem to provide the privacy the monk seals need to survive. Occasionally, individual monk seals will try to rest on beaches of the main Hawaiian Islands, particularly those on Oahu and Kauai, but do not tend to stay very long as they appear to be extremely sensitive to intervention by humans.

Adult monk seals measure about seven feet in length and weigh between 400 and 600 pounds, with females often being larger than males. While at the breeding islands, monk seals feed on bottom and reef fishes, octopuses, eels, and spiny lobsters found in relatively shallow waters close to shore. So much time may be spent at sea that monk seals, when seen on beaches, appear to have green fur. This green color is actually a type of marine algae which has grown in their fur.