The elite

The Sangheili (Latin Macto cognatus, meaning "I honor my father's blood") are a reptilian (or theropodian) species of fierce, proud, strong, intelligent warriors and skilled combat tacticians. Sangheili are named after their home planet, Sanghelios. Known by most Humans as Elites, presumably due to their adeptness and their skills in combat, the Sangheili formed the military backbone of the Covenant for almost the entirety of its existence. They had a rivalry with the Brutes, which became hatred during the Great Schism and the conclusion of the Human-Covenant War.i have got this info from halopedia.com

Originally a founding member of the unified conglomerate of races known as the Covenant, they later led the Covenant breakaway faction known as the Covenant Separatists due to the fact that the Prophets ordered the genocide of their entire race. This was established after the assassination of the Prophet of Regret by the hands of the "Demon." It was the Sangheili who were ultimately held responsible for the Prophet of Regret's death, and were seen as "unfit" to continue to guard the Prophets. The Prophets sought to achieve this through the use of the other Covenant races, primarily the Brutes. The aftermath of the Great Schism formed the bedrock of the Covenant's ultimate collapse.I have got this info from halopedia.com