Arbiter is a fictional ceremonial, religious, and political rank bestowed upon alien Covenant Elites in the Halo science fiction universe. In the 2004 video game Halo 2, the rank is given to a disgraced commander as a way to atone for his failures. Although the Arbiter is intended to die serving the Covenant leadership, the High Prophets, he survives his missions and the Prophets' subsequent betrayal of his kind. When he learns that the Prophets' plans would doom all sentient life in the galaxy to extinction, the Arbiter allies with the Covenant's enemies—humanity—and stops the ringworld Halo from being activated. The Arbiter is a playable character in Halo 2 and its 2007 sequel Halo 3; a different Arbiter appears in the 2009 real-time strategy game Halo Wars, which takes place 20 years before the events of the main trilogy.
The appearance of the Arbiter in Halo 2 and the change in perspective from the main human protagonist Master Chief to a former enemy was a plot twist Halo developer Bungie kept highly secret. The character's name was changed from "Dervish" after concerns that the name reinforced a perceived United States versus Islam allegory in the game's plot. Award-winning actor Keith David lends his voice to the character in Halo 2 and 3, while David Sobolov voices the Arbiter of Halo Wars.
The Arbiter has appeared in three series of action figures and other collectibles and marketing in addition to appearances in the games. Bungie intended the sudden point of view switch to a member of the Covenant as a plot twist that no one would have seen coming, but the character in particular and the humanization of the Covenant in general was not evenly received by critics and fans. Computer and Video Games derided the Arbiter's missions as "crap bits" in Halo 2. Conversely, IGN lamented the loss of the Arbiter's story in Halo 3 and missed the added dimension the character provided to the story.