The Elite known as the Arbiter was previously the Supreme Commander of the Fleet of Particular Justice. However, after failing to stop the destruction of the Halo in Halo: Combat Evolved, he was stripped of his rank and honor. He was branded with the Mark of Shame and was to be hanged by his entrails, with the corpse to be paraded through the city of High Charity. However, the High Prophets understood that he was no heretic, and gave him the chance to restore his honor by giving him the reverable rank of Arbiter. He felt unworthy, but he did accept this rank and the suicide mission that came along with it.

He, to the suprise of the Prophets, survived his first suicide mission to kill a heretic rebel. He was sent on another suicide mission: to unlock the containment shield on Delta Halo's Library and allow the Covenant in. Unknowingly to the Arbiter, the Prophets were replacing the honorable role of the Elites in their caste with Brutes. The Brutes (with the will of the Prophets) had then assassinated most Elites with high-ranking positions. The Brute Chieftan Tartarus was sent to kill the Arbiter if he did survive his mission.

The Arbiter was saved by Gravemind and was told by him (and the Monitor 343 Guilty Spark) that the Halos were designed to destroy all life in the galaxy. Although at first he was unwilling to accept this as the truth, after fighting with the seperatists againt the Covenant for a brief while, he eventually did believe it. In his attempt to stop the Halo from firing, the Arbiter and Sergeant Johnson killed Tartarus. In Halo 3's campaign, he will fight alongside Master Chief, or can be controlled by player two in co-op.