Zile was an upper-level warlock who planned to acquire the power of the Charmed Ones. He was intent on making Prue his wife to further his evil powers. He teamed up with a dark priestess, Dantalian, who was supposedly willing to unite them in unholy matrimony in return for getting the Book of Shadows. The Charmed Ones' magic was so intertwined by this time that Prue's marriage to Zile would turn Piper and Phoebe evil as well, and the evil would flow through to the Book.