The False Prophet is a literary term for a character in DEXTER. The False Prophet is depicted as an agent of "The Beast" and is said to be cast within The Lake of Fire along with its master. According to Travis Marshall, Dexter Morgan is The False Prophet that tried to lead him "astray" from the Path of God. In reality, Dexter believed that Travis was innocent while Professor Gellar was the true Doomsday Killer. In reality, Gellar has been dead from the start and Travis was acting alone while believing in an illusion that he considered to be Professor Gellar.
The term was originally used by Professor Gellar, which in turn means that Travis was thinking this deep down but refused to believe it because he was currently suppressing his darkness in the form of Gellar. After realizing the truth about Gellar and himself, Travis has consistently named Dexter The False Prophet.