Summary
The Prophet of Disdain is only known from a Halo 2 match held at E3. In it, players used premade accounts with the names of Halo characters. One team played as Spartans and used Marine names, the other team as Elites and using Prophet names including "Disdain".
It is unknown whether or not he had been planned for Halo 2, but never he made it into the final game.