The leader of the "five dusky phantoms," whom Ahab has secretly brought aboard to serve as his private boat crew, is the mysterious Fedallah, who serves as the captain's harpooner. An ancient Asian, he is reported to be a Parsee — a member of a religious sect descended from the Persians and devoted to the teachings of the prophet Zoroaster in the sixth century B.C., contrasting the spirits of light or good (Ormazd) with the spirits of darkness or evil (Ahriman). Here, the significance is that Fedallah is a man of mystery, a non-Christian who seems to be Ahab's guide or guru. Some critics suggest that, because Fedallah is a Parsee and supposedly devoted to good, he is a double agent, an assassin sent by God to eliminate Ahab. (If one considers that the Parsees were "devoted to "doing God's work" as opposed to "devoted to good," it is possible that Fedallah is doing both. Given Ahab's perspective of God and the universe, this interpretation of Fedallah and his role is valid.)
Through his actions, though, Ahab's guide seems more demonic — perhaps a Parsee who shares Ahab's madness and perceives the same evil that the captain sees. In either case, Fedallah contributes to the rich ambiguity surrounding Ahab. The Parsee's prophecy regarding the captain comes true in surprising ways near the end of the novel.