Sangheili, or as humans call them "Elites", are a type of alien that fought against the humans in the Human-Covenant war, but allied with them during the great schism, an event were the Sangheili were betrayed by the Covenant. A notable member of the Sangheili society Is Thel Vadam, better known as "The Arbiter", is the main protagonist of Halo 2, and an ally in Halo 3. Sangheili appear in all Halo games, except ODST.
The Elites are the Covenant and Human title for the Sangheili (Macto cognatus; "I glorify my kin"), the military arm of the Covenant Empire. They hail from the planet Sanghelios which is in a triple-star system lightyears away from Earth. The Sangheili fought a long war with the San 'Shyuum (Prophets) from 938 B.C. to 876 B.C. over the treatment of Forerunner relics, the Elites believing that they should be revered and left untampered while the Prophets thought they were gifts from the gods and should be used for the good of their race. With the Prophets' prowess in space combat due to their Forerunner Dreadnought, the Elites came to the conclusion that they must use the Forerunner relics scattered across their own planet to tip the scales of the war in their favor, which is what the Prophets had been doing all along. With the whole reason the war began now thrown aside, the two species formed a shaky alliance with soon evolved into the Covenant. In 2552, near the end of the Human-Covenant War, a civil war between the Elites and the Covenant began, with the Jiralhanae (Brutes) taking over for the Elites. The Elites formed the Seperatists while any Covenant species that still believed in the Great Journey, the effort to fire the Halo Array to transcend into god-hood, were known as the Loyalists. Siding with the United Nations Space Command, the Seperatists played a large role in the defeat of the Loyalists and the Flood. Throughout the series, the Elites are constantly seen leading the lesser species of the Covenant into battle. They don blue, red, white, black, or golden armor depending on their rank and use energy and plasma weapons in battle. They are very intelligent and strong, as they are capable of outflanking and defeating the player fairly often. Their honor and loyalty combined with religious fanaticism ensures that they rarely flee from combat, even when facing impossible odds.