Moby Dick is a sperm whale. According to Wikipedia: The sperm whale (Physeter macrocephalus) is a large toothed whale (odontocete) belonging to the order Cetacea. You can read more about Moby Dick and sperm whales by referring to eNotes Study Guide for Moby Dick on the reference link below, particularly to the Summary section. You can also refer to sperm whales on the internet for complete descriptions. Although sperm whales are dark in color, Herman Melville made Moby Dick white. Some critics attach symbolic significance to this white color, but chances are that Melville had a plot problem to solve. How were the sailors going to recognize Moby Dick when they saw him? That is why Moby Dick is often described as "the great white whale." Male sperm whales are very large. One of them actually sank a whaling ship.
Moby Dick was a sperm whale.