A member of the triumvirate that heads the Covenant (the other two being the Prophet of Mercy and the Prophet of Regret), the High Prophet of Truth is the most vocal about the importance of the "Great Journey"—a Covenant euphemism for the activation of the Halo rings. He decides to spare the life of the Arbiter, allowing him to continue to serve the Covenant. However, after the Prophet of Truth orchestrates the replacement of the Elites—the Arbiter's race—with the Brutes, and after learning the truth of the Great Journey, the Arbiter switches sides, and Truth's mercy proves to be his undoing.
After leading loyalist Covenant forces in an assault on Earth, Truth discovers the Ark, a construct from which he will be able to activate all the Halo rings at once. He is unable to accomplish this, however, and the ironically named voice of Truth is silenced by the Arbiter's sword.