Along with the Prophet of Truth and the Prophet of Mercy, the High Prophet of Regret was a member of the triumvirate leading the Covenant. Being the youngest of the three, his actions were often brash and headstrong. In Halo Wars, he planned to activate a fleet of ancient warships, but he failed when the fleet was destroyed by the human forces. In the main Halo series, he recklessly attacks Earth with a small flotilla of Covenant ships on a quest for the Ark, a place important to the Covenant cause.
When his attack fails, he retreats to a newly-discovered second Halo artifact. There he meets his demise at the hands of the Master Chief. The failure of the Elites to protect the High Prophet causes a schism within the Covenant which eventually leads to the Covenant Civil War.