Many of the alien species conquered by the Covenant are conscripted into, or gradually become part of the alliance. However, during the first contact with the humans, the Oracle on board the Forerunner dreadnought revealed to Truth and Regret that Humans are Reclaimers, as shown by its luminary. Since the entire Covenant was based on the belief that the Forerunners had transcended, Truth and Regret knew if any of the other races found out what the Oracle told them, the Covenant would cease to exist.
The highest caste, the San'Shyuum, or "Prophets" as Humans call them, lead the Covenant and exert complete control over all religious and political affairs. Though physically weak, Prophets wield power through absolute command of the Covenant and through scavenged Forerunner technology, leaving the task of conquest to the Sangheili and the other races. Their higher understanding of the Forerunners gives them great ego and religious influence over the Covenant. The High Prophets are addressed as "Hierarchs," "Noble Hierarchs," "Holy Ones," or "Exalted" by the other races of the Covenant.
The second highest caste; Sangheili, or Elites as Humans call them, served as the military leaders of the Covenant before the Great Schism in 2552. While Prophets often had the final say, it was the Sangheili who organized military campaigns and naval engagements. They maintain the military structure of the Covenant and ensured the Prophets' orders are followed, as well as their own. Sangheili consider the other client races to be below them in all ways. The Sangheili are the only known race permitted to build and operate starships within the Covenant, though the crews are almost always composed of a mix of races. Sangheili are separated into ranks based on skill and experience. To advance in rank, Sangheili must honorably earn such advancements on the battlefield. They were a major component of the Covenant and were the only caste able to maintain the military hierarchy as well as having a voice within the High Council before the Great Schism. An "ee" at the end of a Sangheili name, such as "'Zamamee or 'Vadumee," signifies that that Sangheili is a part or was part of the Covenant military, although, after the Great Schism most, if not all, Sangheili removed the "ee" from their names to show that they had left the Covenant.
Jiralhanae, known to Humans as Brutes, They are one of the newer species to the Covenant and are the only race that has obtained very close to equal status to that of one of the founding "clients" of the Covenant pact, the Sangheili. They have an incredible natural resilience to damage due to their tough hides, which easily make up for their lack of energy shields, and use a number of weapons and vehicles based upon their pre-Covenant technology. This technology, though primitive compared to other Covenant weapons, is nonetheless extremely lethal, with most Jiralhanae-developed weapons having blades attached to them. In addition to their standard form of combat, Jiralhanae will sometimes go "berserk" and try to kill anyone or anything in their path. This shows the aggressive nature of the Jiralhanae, and the little tolerance they have when they are cornered. Jiralhanae have their own ranks going up to War Chieftains who usually wield plasma cannons, fuel rod guns, or Chieftains who usually wield gravity hammers. The Jiralhanae always work in packs of 3-8 when possible. They took over the role as personal bodyguards of the Prophets and also now make up most of the Covenant military.
Huragok, or Engineers, are actually an artificial species created by the Forerunners. They will only converse with the Prophets or individuals who learn their language. This indicates Engineers are very high in the caste system, however ONI believe them to be prisoners or slaves. The Huragok perform the physical labor of excavating, and gathering data on Forerunner artifacts. In military terms, they are generally a non-militant race. However, at times in the Human-Covenant war they have been placed on the battlefield either as repair workers or suicide bombers. They have also displayed neutrality and even some allegiance to humans such as Lighter Than Some helping the citizens of Harvest escape and another Engineer repairing Ascendant Justice's engines for John-117 and even a Needler for him to use in battle. Another example is one Huragok repairing and recovering the Human AI Superintendent and then assisting Captain Veronica Dare and Sergeant Major Avery Johnson in working out what the High Prophet of Truth was looking for in Africa. It was also revealed that they are equipped with a personal energy shield only when they are under duress. Additionally, these Huragok are also able to project an energy shield around its allies, or enhance shielding already present, if they are within its proximity.
Mgalekgolo, or Hunters as they are known by Humans, are thought to be giant monsters, but they are actually an assemblage of worm-like entities called "Lekgolo" that creates a large, armor plated form. In this form, they are known as "Mgalekgolo." They always fight and travel in pairs known as "Bond Brothers" which technically means that not all of the colonies of worms were able to fit within one set of armor, and are the strongest of the Covenant fighting units. They wield powerful assault cannons and a massive shield resistant to any small arms fire which may also be used as a melee weapon due to its sharp sides and the Mgalekgolo's great strength. They are usually used as weapons platforms, and are only deployed on the battlefield when in need of a heavy force - they are used more like heavy duty equipment than soldiers. Their political and religious motivations are completely unknown.
These flying insect-like creatures, also known as Drones or Buggers by Humans, served almost exclusively as engineers, but were then replaced by the Huragok. This created a hatred towards the new, peaceful engineers by the Yanme'e that sometimes resulted in violence. Afterwards, the Yanme'e were used as aerial combatants against the UNSC, who were inexperienced at fighting airborne infantry. In combat, their weapons of choice were the Needler, which creates a super-combine explosion if enough projectiles are fired into the same target, and the Plasma Pistol. Their ability to fight on the wing, and their usual deployment in large groups, made them an excellent strategic weapon against ground-based opponents.
Due to their superior senses, the Kig-Yar, or Jackals/Skirmishers as they are known by Humans, are the scouts and marksmen of the Covenant military, they are the second lowest Covenant caste. Due to their lack of physical durability, they carry a portable energy shield generator during combat. Kig-Yar are employed mainly as sharpshooters with their excellent vision and dexterity, and are also deployed to defend strategic areas. When a Kig-Yar is under fire, it will cover its head with its hands and trot away to another position from which to fire. The first Human contact with the Covenant was between Staff Sergeants Johnson and Byrne on a Human freighter as Kig-Yar pirates tried to board the ship. The Kig-Yar have very strong dislike of the Unggoy because they are always trying to assert their superiority over them in the caste system of the Covenant. Once they poisoned a recreational narcotic that the Unggoy use which nearly caused them to become infertile. This caused the Unggoy Rebellion.
Hailing from Balaho, Unggoy, known as Grunts among Humans, are the most common and lowest-placed caste of the Covenant. The Unggoy were barely into their own Iron Age when the San'Shyuum discovered them. Classified as a "Tier 6" civilization by the Forerunner charts, the Unggoy were at a primitive point in their cultural development, the Unggoy had little choice but to accept entry into the Covenant hegemony, or otherwise risk extinction. After their incorporation into the Covenant their entire history was erased and they essentially became a slave race. Despite their notable cowardice and ineptitude, they are quite dangerous in large numbers, which was why an Arbiter was needed to quell the Unggoy Rebellion. They breathe methane and thus must wear a large tank on their back full of the methane to survive on other planets. Relations between the Unggoy and the Kig-Yar are strained in the best of times.
Halo is a military science fiction first-person shooter video game franchise managed and developed by 343 Industries, a subsidiary of Xbox Game Studios. Halo was originally developed by Bungie Studios. The series centers on an interstellar war between humanity and an alliance of aliens known as the Covenant.
The games in the series are critically acclaimed, with the original considered the Xbox's "killer app".