Very little information about the Unggoy prior to the activation of the Halo array survives to the modern era, but it is known that theirs was a Tier 4 society. However, they never became spacefaring due to a number of factors. Their species' rapid breeding cycle led to a population crisis on their homeworld of Balaho, which was reflected in and compounded by the near complete collapse of the planet's biosphere due to global industrialization.
Balaho's atmosphere and hydrosphere were severely damaged by industrial waste. It's speculated that the planet was home to thousands of fish and avian species prior to industrialization; afterward, eight out of every ten species was driven to extinction. Naturally, this led to a shortage of basic resources necessary for survival, which in turn began a brief but devastating resource war that left the Unggoy all but bereft of any means of self-sufficiency. Entire clans were destroyed, cities razed and any semblance of government was nonexistent; they had fallen into a state of self-preservation and no longer possessed the resources to lift themselves back up from the pit they had thrown themselves into.
Ancient Unggoy being reseeded on Balaho by Forerunner machinery.
The Unggoy were one of many sentient species indexed by the Librarian for preservation on Installation 00 from the firing of the Halo Array, after which they were returned to their homeworld where they began rebuilding their culture, though they never regained their pre-Halo status. The highest they achieved was Tier 6, having just rediscovered electricity when the Covenant found them.
Despite never being depicted as a target of the Flood in any of the games except Halo Wars, it's meant to be assumed by the fans that they were just as threatened by the parasite as every other species in the Milky Way.
Unggoy being taken from their homeworld, Balaho for incorporation into the Covenant.
Not including San'Shyuum and Sangheili, Unggoy were the sixth client race to be integrated into the Covenant, coming to their indoctrination at around 2142 on the Military Calendar. By the time of their discovery by the Covenant, the Unggoy homeworld was still recovering from its ecological collapse over a hundred millennia earlier, and the Unggoy civilization had yet to return to its former state.[4]
While they are essentially a slave race, the Unggoy have managed to largely retain their cultural identity and rebelled in the past several times. Being the lowest-ranked species of the Covenant, they are bitter rivals with the Kig-Yar, the next lowest-ranking species. The higher-ranking races of the Covenant have often been content to ignore this rivalry. The breaking point came when a junior staffer in the Ministry of Concert[5] discovered evidence of the Kig-Yar planning to poison recreational narcotics the Unggoy enjoyed, which would have left them sterile, but the High Council refused to investigate the matter. The rising tensions with the Kig-Yar and the general disinterest of the other Covenant races to intervene led to the Unggoy Rebellion in 2462. While the rebellion was ultimately put down thanks to an Arbiter and the near-glassing of the Unggoy homeworld, the Unggoy proved that they were not the cowards they had long been perceived to be, and could indeed be vicious fighters when provoked. After the uprising's conclusion, as was their tradition, the Sangheili forgave the surviving Unggoy and allowed them to enter the Covenant military as armed infantry units, rather than the unarmed cannon fodder as which they had previously served.[6]
Despite the low position they occupy in the Covenant Hierarchy, the true irony is that the Unggoy's entry into the Covenant has ensured their species' survival. Membership in the Covenant granted the Unggoy freedom from risk of extinction during Balaho's two winters, as they now have access to sufficient supplies of food. Infant mortality has decreased to below fifty percent since joining the Covenant, and geronticide is no longer a necessity for survival. The average life expectancy for non-combatant Unggoy has doubled.[7] Their incorporation into the Covenant likely also alleviated the threat of the Blue Death, which Unggoy typically fear.[8]
The Unggoy obey other Covenant races out of fear more than faith or loyalty.[9] They have next to no political power in the Covenant; the highest political rank an Unggoy can hope to achieve is Deacon, and the Unggoy community harbors a strong resentment toward other species, especially the Kig-Yar. Their low rank, cruel mistreatment and the aforementioned war also led to a lack of political loyalty during the Great Schism, as they didn't ally with a particular side, and stayed with whoever commanded them, most likely out of subservient fear to their current masters. However, many of those serving under the Jiralhanae still held support for the Sangheili and revered the Arbiter, pointing out to their comrades that they once served under him.
Unggoy are poor warriors in terms of skill and physique. Their focus is nominal at best, their natural posture inhibits quick movement, they lack any meaningful tactical or strategic ability and their constitution is generally unsound. When witnessing their commanders eliminated during a battle, they often go into a panic and scatter in random directions. However, what they lack in skill and prowess they make up for with sheer numbers and tenacity; also if they are focused, can be quite accurate with their weapons not to mention they breed at a remarkable rate. The Covenant used the high-breeding rate of the Unggoy to their advantage in the Human-Covenant War, where squads of Unggoy very frequently overpowered UNSC personnel through weight of numbers alone. The conflict on Harvest, and thus the Human-Covenant War, was in part started by an Unggoy named Yull tearing apart Private Osmo. Special Operations Unggoy, known for their dark armor, are far more tenacious than the lower tiered ones and have even been known to carry fuel rod guns and plasma launchers which makes them extremely dangerous foes, it should also be noted, that these fuel rod-wielding Unggoy can fire their massive weapons without needing to stabilize them with their other hand.
Unggoy are the only species known to breathe methane rather than oxygen. Their combat harnesses have integrated methane breather systems, as they are unable to survive long periods without methane due to asphyxiation much like humans without oxygen. Therefore, if the player manages to knock their methane tank off in a melee attack they will die after a short amount of time. Also, it is possible in Halo: Reach to shoot the vents on either side of the tank, resulting in the tank popping off and the Unggoy becoming airborne.
An Unggoy Heavy prepares to fire his Fuel Rod Gun.
Fairly intelligent, cowardly and not very creative on the battlefield, Unggoy are one of the most gregarious and sociable of the Covenant races and possess a very strong pack mentality, often associating with each other in groups. Although quite capable of operating weaponry, vehicles and machinery such as Ghosts and Shades, Unggoy are thought to be unintelligent. This is most likely due to stereotyping created by higher-ranking species such as Sangheili and Jiralhanae, who have grown accustomed to expecting blind obedience from subordinates.
There are exceptions to this rule, however: The Unggoy Deacon Dadab, for example, was noted as being quite intelligent for an Unggoy, as demonstrated by his ability to learn and communicate in Huragok sign language; however, this is simply because he was allowed to be intelligent by his superiors. An Unggoy can be found on the farm lands of the Sangheili homeworld Sanghelios. They sometimes use a recreational drug in the form of a gas they mix into their methane tanks called infusion, sometimes referred to as "the gas." It was found by ONI operative Evan Phillips.
The Unggoy seem to outnumber the other races to a large degree and might offer impressive resistance if properly organized. They have been called "cannon fodder" because their Sangheili or Jiralhanae leaders will often send them out to serve as a distraction, rather than actually having them effectively engage an enemy in combat. This numerical superiority and pack mentality allows for their sense of cultural identity to remain, despite a number of hardships, including their extreme subservience to the other races of the Covenant, as well as the dark time following reintroduction after the activation of the Halo Array.[4]
An inherent psychological advantage possessed by the Unggoy are their unburdened neural pathways, which allow the Unggoy to absorb knowledge more freely compared to the other Covenant species. As such, they are often tasked with monitoring space for traces of human communication. In addition, many Unggoy have developed a clear understanding of two or even three human languages. This advantage serves as a river of confidence in times of great stress for them.[4]
Unggoy generally follow a few short, simple guidelines given to them by the Sangheili, namely "when in doubt, shoot," or "stay out of the way, live another day." Despite being held in low stature in the Covenant, many Unggoy appear to be strong followers of their religion. Their Deacons will often hold sermons onboard ships to boost the morale and teach the Unggoy onboard about the Covenant. For instance, a Deacon named Dadab gave sermons and taught the Unggoy on board a Jiralhanae cruiser about the Covenant and its religions. The Jiralhanae allowed Dadab these teachings because they believed that it would help the Unggoy become more competent and helpful.
They often gamble with each other and play games. One in particular, hunting rock, involves two Unggoy competing to kill the most Scrub Grubs. In the novel Halo: Contact Harvest, the Unggoy Deacon Dadab stated that scrub grubs were easy targets compared to the mud wasps and shade crabs of his homeworld.
An Unggoy's luminous blue blood.
The face of an Unggoy Minor.
Unggoy share a number of features with different animal species on Earth. Like primates, they walk both bipedally and with the aid of their oversized forearms in a manner similar to a chimpanzee. Their bodies are armored with a hard exoskeleton, much like crabs and insects. Their mouths have a set of small, pointed teeth, much like reptiles. However, the UNSC has classified them taxonomically as being most similar to Earth arthropods, but being alien in nature, they still aren't technically arthropods.
Unggoy are on average about five feet tall and are relatively weak compared to other species. Although they can easily walk upright on two legs, they may often use their arms to move in a quadrupedal fashion. While carrying armaments, they are forced to walk upright so that they may support their weapons with their hands, but while trying to flee, or while patrolling without a weapon drawn, they use their oversize arms as forelegs to add speed or stability to their gait. Their eyesight and hearing are average and they seem to have a very well-developed sense of smell, sometimes sniffing the air to detect traces of foes or hidden threats.[10] This is facilitated through the olfactory membranes installed in their masks.