Mordred was long prophisized in Mid-world. He was said to be born of two fathers through incest with his daughter/sister. Roland's sperm was taken from him by an elemental demon in the oracle during The Gunslinger. It was taken and mixed with the sperm of the Crimson King. While "drawing" Jake Chambers to Mid-World, Susannah has sex with the hermaphrodidic demon Roland had sex with earlier and is impregnated with the mixed sperm.
Mordred murdered Walter Padick after telepathically detecting Padick's intention of using Mordred's birthmark to enter the Dark Tower.Mordred follows the Ka-tet of Roland for a long time, having multiple opportunities to attack. Finally when it is just Roland, the artist Patrick Danville, and the billy-bumbler Oy, Mordered attacks. Oy sacrifices his life for Roland, allowing the gunslinger to shoot and kill Mordred close to the fields of Can-Ka-no-rey. He is named after the betrayer of Arthur.