Thel 'Vadam, known during the later Human-Covenant War as The Arbiter and the Necros War as The Imperator, was a distinguished Sangheili. After being stripped of his rank of Supreme Commander after the Battle of Installation 04, he became the Arbiter, survived multiple attempts on his life by the Covenant Loyalists, and then assisted John-117 in killing the High Prophets and destroying the Ark.