The Covenant were first introduced in Halo: Combat Evolved as the protagonist Master Chief and the AI Cortana are escaping from the UNSC ship Pillar of Autumn in orbit over Halo; the Covenant disable the ship and board it via landing craft. On Halo, the player encounters the Covenant in force all over the ring, and they are the primary enemies until the Covenant release the Flood from stasis. To develop a distinctive look for the various races of the Covenant, Bungie artists drew inspiration from reptilian, ursine, and avian characteristics. A Covenant design scheme of purples and reflective surfaces was made to separate the aliens from human architecture.
The Covenant's society and internal workings are elaborated on in Halo 2, with half of the game's single-player campaign taking place from the perspective of a Covenant Elite, the Arbiter. The Arbiter and two other Covenant characters, N'tho 'Sraom and Usze 'Taham, are playable in Halo 3s four player co-op; however, only the Arbiter is present during cutscenes and single player mode.
During the course of development of Halo, the designers decided upon three "schools" of architecture, for each of the races represented — the humans, Covenant, and Forerunners. For the Covenant, the team decided on "sleek and shiny", with reflective surfaces, organic shapes, and use of purples. According to art director Marcus Lehto, the principle designs for the race came from environmental artist Paul Russell.
Like the character designs, Covenant technology, architecture, and design continually changed throughout development, occasionally for practical reasons as well as aesthetics. According to Eric Arroyo, the Covenant cruiser Truth and Reconciliation, which plays a major role in Halo: Combat Evolved, was to be boarded by the player by a long ramp. However due to technical considerations of having a fully textured ship so close to the player, the designers came up with a "gravity lift", which allowed the ship to be farther away (thus not requiring as much processing power for detail) as well as adding a "visually interesting" component of Covenant technology.
The art team also spent a large amount of time on Covenant weaponry, in order to make them suitably alien yet still recognizable to players. At the same time, the designers wanted all aspects of Covenant technology, especially the vehicles, to act plausibly. Bungie ended up looking at movies and other media for inspiration on almost every aspect of the race.
The Covenant's superior technology allow them to annihilate the human Outer Colonies within four years; the Covenant begin to destroy the Inner Colonies in short order as well. However their efforts are stymied by the Cole Protocol, which stops UNSC ships from directly or indirectly traveling to inhabited human worlds (forcing them to make several random trips before actually returning to a human colony) and upon imminent risk of capture, the ship's AI is erased with the rest of the navigational database, and the ship self-destructs. In 2552, the Covenant assault the human colony Sigma Octanus IV in an effort to recover an ancient artifact with Forerunner glyphs on it, but are repelled by a UNSC battlegroup. Victorious, the Iroquois departs the system; unbeknownst to its crew or the UNSC, a Covenant transmitter attaches to the Iroquois and reveals the location of Reach, Earth's best defended colony, to the Covenant. A massive Covenant fleet arrives at Reach and lays waste to much of the planet.
Halo: First Strike describes the Battle of Reach from the Spartan team's perspective, and also of the immediate events following the destruction of the first Halo. Later, the Master Chief and his fellow SPARTAN-IIs, recovered from the remains of Reach, destroyed the Unyielding Heirophant and a Covenant Armada estimated at over 500 ships strong that was to attack Earth.
At the same time, the Covenant is experiencing stress. The death of Regret leads to the remaining Prophets transferring the Brutes into the position of their Honor Guards, a job the Elites had previously held, claiming that Elites could no longer guarantee their safety. This sudden displacement severely angers the Elites, who had been in such a position since the founding of the Covenant, and they threaten to resign from the High Council; the Prophets give the Brutes carte blanche to murder the Elites, sparking a civil war. The Elites join their former enemies, humanity, in stopping the firing of Delta Halo; Truth, the last High Prophet after Mercy is assimilated by parasitic Flood, leaves High Charity for Earth.
In Halo 2, the central component of the Covenant's beliefs is revealed to be the "Great Journey", a spiritual equivalent of the rapture and the ultimate goal of the Covenant. The Covenant believe that their forebear, the Forerunners, used the Sacred Rings to cleanse the universe of all that was unworthy, and led them to salvation. The Covenant wish to wipe out humanity and the Flood, and follow the Forerunners to their mysterious destination. The Covenant's execution of the Great Journey consists of the activation of at least one Halo installation, the "divine wind" of which will sweep all those who are worthy on the path to the beyond.
As revealed in Halo: First Strike, Covenant weapons are based on Forerunner technology. Plasma weapons are built around a battery that generates plasma and discharges it at a target. Frank O'Connor, Bungie' former Public Relations head, hinted that there may be something more to the Covenant's weaponry, saying: "The actual technology is not plasma as we know it, but something far more dangerous, arcane, and destructive. A few of the Covenant's weapons are not plasma-based, including the Needler, which instead shoots razor-sharp pink needles capable of homing at organic foes. The Needler was featured in an Electronic Gaming Monthly article discussing the practicality and historical basis for fictional weaponry; a weapons expert noted parallels between the Needler and ancient Amazons painting their daggers pink as a psychological weapon.
Prior to the formation of the Covenant, the Prophets faced utter defeat by the Elites. It was not until the discovery of Forerunner artifacts on the Prophet home world that the two sides were able to form a peace treaty, thus laying the foundation for the Covenant. Since then the Prophets have put considerable effort into extending their own lifespans, as well as breeding to preserve specific genetic traits. These eugenics effort involve declaring many individuals unable to breed, not from unfitness, but because their traits are already too common. After their home world was destroyed, the majority of the Prophet population began to reside within High Charity and its surrounding fleet. After the outbreak of the Flood within High Charity as well as the Elites' turning against the Prophets, their population has dwindled to near-extinction levels.
The Prophets were primarily designed by Shi Kai Wang and Eric Arroyo. Originally, the Prophets were designed in a more unified way, with their gravity thrones fused with the Prophet's organic structures. The characters were also designed to be feeble, yet sinister. The three Prophet Hierarchs were each individually designed.
One of the Elites' standout features is a four-part lower jaw. Early in Halo: Combat Evolved's game development, and in the E3 2000 promotional video, the Elites had more simple jaws and carried shields instead of the personal shields they came to use.
The Brutes have a long-standing rivalry with the Elites, due in great part to the Brutes' unquestioning loyalty to the Covenant religion and, in turn, the Prophets. This animosity eventually culminates into civil war between the two sides and splits the Covenant in two. Simultaneously, the Brutes fill the void of the Elites' departure from the Covenant, assuming leadership roles within the Covenant military and becoming the sole protectors of the Prophets. Prior to their new position in the Covenant, the Brutes primarily acted as occupying muscle, and thus were rarely seen by humans prior to Halo 2 except on Harvest.
Though not a significant threat to the player on their own, Grunts rarely fight by themselves. When in large groups and emboldened by a higher-ranking unit, such as an Elite, they can overwhelm any opponent with massed fire or through sheer numbers. The Covenant views Grunts as disposable in nature.
Each Hunter entity is actually a conglomerate colony of sentient orange symbiotic worm-like entities, held together by their armor. This grouping allows the normally unintelligent eels to work together, dramatically increasing their overall intelligence and strength. Hunters that fight in pairs (as all Hunters encountered in the game do) are considered to be "bonded"; that is, both hunters are actually part of a single colony that is too large to fit inside a single suit of armor and thus must occupy two suits. Individual eels are seen used in Contact Harvest to "map" the insides of Forerunner technology where normal workers could not reach. The eels' fondness for burrowing through Forerunner architecture is the reason for their introduction into the Covenant; after the Covenant failed to destroy the eels for their desecration of sacred relics, the Arbiter of the time suggested "taming" the Hunters instead. Hunters do not take part in Covenant activity outside of battle, as they only remain within the Covenant so as to utilize its space travel technology.
Engineers (Forerunner: Huragok) are the scientific engineering backbone of the Covenant and its economy. The name Huragok was given to them by the Forerunners themselves, indicating their Forerunner connection; most Engineers are found residing within Forerunner facilities, and, as indicated in Halo 3's Beastiarum, were created by the Forerunners. Despite this connection, they have been unhelpful in divulging the secrets of their creators, as they are more concerned with an item's repair than its function or purpose. Parent Huragok fill their offspring with an arrangement of gases and name them accordingly, such as Far Too Heavy or Easy To Adjust or Lighter Than Some.
Engineers float via air sacs and their tentacles are able to split into many fine cilia, with which they are able to manipulate machinery. Their motivations are unknown, but they appear to draw no distinction between friend and foe, preferring to spend their time inspecting or repairing technology. They will, however, utter a high pitched keening sound when a Forerunner artifact is under any sort of threat. Their vocal range is limited to screeches and small chirps, which they only use to alert or add emphasis. Their actual language is communicated in sign, using their tentacles to make words. With practice, others can learn to read Engineer signing and duplicate their language using their own fingers as analogs for the Engineers' tentacles. Additionally, an Engineer's float-bladders will pulsate differently depending on an Engineer's mood. While their language can be learned, it seems that few other members of the Covenant have the patience or need to do so, as the Engineers typically carry out their tasks of examining and maintaining technology of any sort without external direction. Engineers can repair themselves or others of their kind assuming there is no significant damage, allowing them to theoretically extend their lives indefinitely.
Drones (Covenant: Yanme'e) are the only insectoid race within the Covenant. Drones first appear in Halo 2 as new additions to the Covenant fighting force, though Contact Harvest explains the Drones are previously used as mechanics when Engineers are not available.
The Drones, like the Grunts, are a conquered race that was forced into service by the Covenant. They strictly follow Covenant religion and obey unquestioningly, but do not take part in social norms due to a difficulty in communication with other species. They view the Prophets as their "queens", a remnant of their former hive lifestyle.