The narrator of Moby-Dick calls himself "Ishmael", the name of the first son of Abraham in the Old Testament. The Biblical Ishmael was born to a slave woman because Abraham believed his wife, Sarah, to be infertile; when God granted her a son, Isaac, Ishmael and his mother were turned out of Abraham's household. The name has come to symbolize orphans and social outcasts. One tradition among Arabs claims their descent from Ishmael, much as Jews claim descent from Isaac. The name "Ishmael" still occurs occasionally as a given name though not frequently in the English-speaking world.
Significantly, all of "Ishmael"'s crewmates have biblical-sounding or otherwise artificial names, and the narrator deliberately avoids specifying the exact time of the events and some other similar details. These together suggest that perhaps we should understand the narrator--and not just Melville--to be deliberately casting his tale in an epic and allegorical mode.
Ishmael resembles Melville himself in many ways, as well as the narrator of Melville's White-Jacket: The World in a Man-of-War. All are literary, reflective types who see their shipmates as exemplars of human nature and the universe, and tell their stories with a wealth of philosophical reflection. "White Jacket" is--as symbolized by the garment that gives him his name--very much an outsider to his crew. Ishmael himself sometimes completely vanishes into Moby Dick: toward the end of the novel it can be easy to forget that it is being told by a first-person narrator and not simply an omniscient narrator. However, from the beginning Ishmael tells us that he turns to the sea out of a sense of alienation from human society. In many ways the Pequod is a ship of outcasts that manage to form a complete society among themselves. Ishmael is perhaps its voice, or its self-consciousness.