The rank of Arbiter, in the video game Halo 2, is bestowed upon a Covenant Elite (Sangheili) by the High Prophets of Truth, Mercy, and Regret during a time of need. The Arbiter acts as a sort of field general, going on missions for the Prophets and during incidents such as the Taming of the Hunters, the Grunt Rebellion, and most recently, the threat of Heresy, he has emerged to lead the Covenant to victory. Many, especially Grunts, see the Arbiter as their Savior, and their peers consider him the 'Will of the Prophets' or, in his military role, the 'Blade of the Prophets'. Every Arbiter was 'created and consumed in times of extraordinary crisis', and has been martyred in the undertaking of his momentous tasks. The corpses (or perhaps only memorials of some sort) are housed in identical caskets stacked upon each other in the great Mausoleum of the Arbiters; in the center of this room a floating pod contains the sacred armor of the Arbiter, highly decorative and fully functional despite its apparent age. The mausoleum houses 168 visible caskets (and more may be set underground), reaching high into the air, and references of Arbiters settling the Grunt Rebellion and aiding the Taming of the Hunters would indicate that the office has existed for quite some time - before the Covenant as we know it was fully formed and its castes defined. Seeing how the Arbiter can only be an Elite (the characteristic armor is tailored to the Elite anatomy), it is not unlikely that the tradition of calling upon the Arbiter existed as a part of Sangheili culture before the species joined the Prophets in the Covenant, but this is of course pure speculation.

As a member of the Covenant, it is believed that the Arbiter is held in the capacity of maintaining the integrity of the Covenant. The only three events know to warrant an Arbiter were the Taming of the Hunters, the Grunt Rebellion, and the Guilty Spark Heresy of Installation 04; the Arbiter is required to a) convert/assimilate a new race, b) bring a renegade race back to the faith, or c) destroy separatist portions of the largely stalwart races. Of course, he also serves as a political tool, an embodiment of the Hierarchs' power as well as an example of true faith, a warrior-martyr showing loyalty at the aforementioned times of division.

In the events of Halo 2, the Arbiter's role is filled by the "incompetent" Elite commander of the Particular Justice Fleet, the fleet that followed the Pillar of Autumn to Halo. The Arbiter was the one who lost the Ascendant Justice to Master Chief in Halo: First Strike (whereas Orna Fulsamee was in command of the Truth & Reconciliation). Because the Elite commander failed to protect the 'sacred ring' from the humans, he was branded with the Mark of Shame and sentenced to be hung by his entrails, his corpse to be paraded through the holy city of High Charity. However, rather than have him slain outright, the Prophets of Truth and Mercy gave him a chance to regain his lost honor and serve the Covenant again. He donned the armor of the Arbiter and became the Covenant's equivalent to the UNSC's Spartan IIs including the Master Chief.

As the Arbiter, the Prophets expected this Elite to die in certain crisis, during the Heresy-quelling on Threshold, but he kept living, and fighting whatever threatens the Covenant.

During the game, the Prophets slowly begin to replace the Elites with Brutes, and eventually they call for a genocide of all Elites so that Brutes may replace them in society: a New Order of Imperial Government. This sparks a Covenant civil war. On one side, there are the loyalists: the Brutes, the Drones, and the Jackals, led by the Prophets. On the other, the Elites lead the Hunters and the Grunts. The Arbiter, being an Elite, after meeting the Master Chief while being held captive for interrogation by Gravemind naturally sided with these separatists and became a central figure in the Covenant civil war. This breakaway faction even manages to secure an uneasy alliance with their enemies, the Human United Nations Space Command to stop the mutual threat of the Halos being set off.

At the end of the game, the Arbiter engages Tartarus, the Brute Chieftain, in combat over the Index and the detonation of Delta Halo. With the aid of Sergeant Johnson, the Arbiter triumphs.