- "Oh, but what I would not give to have even a single company of Prometheans here right now... oh, they would most certainly restore order with their trademark lethality..."
- —343 Guilty Spark musing to himself as his Installation is about to be destroyed.
The Prometheans were the highest and most respected group of Warrior-Servants in the Forerunner ecumene. During and after the Human-Forerunner War, they were led by the Didact. The Prometheans' main base of operations was the shield world known as Requiem.
During the Forerunner-Flood war, the Prometheans were converted into digital intelligences, known as Knights, by the Forerunner machine known as the Composer. These constructs, along with the Didact, survived the activation of the Halo Array, eventually awakening within Requiem and rising to oppose the UNSC in 2557.
 Original Prometheans
Physically, Prometheans were the highest form a Warrior-Servant could mutate to, standing around two times the height of a Forerunner Manipular and weighing about four or five times a Manipular's mass. They were heavily muscled, their hands capable of easily crushing a human. Their mental capabilities were also very sophisticated; it was common for a Promethean to share information and sensory input with the warriors under their command. Prometheans were also capable of controlling a million remote-controlled craft, such as weapon-ships, simultaneously.
They also used powerful vehicles known as war sphinxes for large-scale operations. In order to combat the parasitic Flood during the Forerunner-Flood war, the Prometheans' arsenal of weapons was specifically tailored to disintegrate targets to prevent the Flood from repurposing any available biomass.
 Known Prometheans
- The Ur-Didact
- The IsoDidact
- The Confirmer
- The Grammarian
- The Strategos
- The Examiner
 Mechanical Prometheans
The Promethean forces encountered by UNSC forces and Covenant remnant insurgents on Requiem are primarily mechanical in nature, and encompass various classes of leader units known as Knights, support drones known as Watchers, and small, pack-oriented Crawlers designed to overwhelm the enemy from different directions. Significantly different from the original Prometheans, these constructs were created by the Didact toward the end of the Flood conflict; in order to render them immune to Flood infection, the Didact used a machine known as the Composer to convert his warriors into digital intelligences; the warriors willingly accepted and were relieved of biological form. However, as the Prometheans' numbers continued to dwindle, the Didact used the Composer on a population of humans transplanted on a Halo installation to create more of these mechanical Prometheans.
Visually, unlike most Forerunner technology which is chiefly angular and geometric, these Promethean units have a more curved, almost biomechanical aesthetic. Various Promethean units, including Knights and Watchers, have distinct heads embedded in their mechanical carapaces, complete with stylized facial features; this feature was shared by the war sphinxes used by the original Prometheans.
- Promethean Knight
- Promethean Crawler
- Promethean Watcher
For thousands of years, the fortified shield world Requiem served as the main command center of the Prometheans. Following the Human-Forerunner War and the discovery of the Flood, the Prometheans, under the leadership of the Didact, stood in opposition to the radical faction of Builders led by Master Builder Faber, who proposed the construction of the Halo Array. They lost the political battle and were subsequently removed from the Ecumene Council, with the Master Builder's allies rising to power in the Council instead. Disgraced, the Didact and some of the other highest-ranking Prometheans were allowed the dignified choice of exile in a Cryptum, while some of the lesser-ranked commanders were accorded more severe punishments.
After a thousand years of exile, the Didact was reawakened amidst the Forerunner-Flood war. Shortly after his revival, a radical shift occurred in the Council, and Faber lost his political power due to his crimes against the Mantle. Called upon to defend the ecumene against the onslaught of the Flood, the new Council elevated the Prometheans back to their former status, and the Didact resumed his duties as the supreme commander of Forerunner military forces. Under the Didact's leadership, the Prometheans would lead the ecumene's defenses against the Flood until the end of the conflict and the activation of the Halo Array. Near the end of the war, the Didact, still adamant in his opposition of the Halo Array, resorted to the use of the Composer, converting his Promethean warriors as well as a number of humans into war machines. Viewing the Didact's conscription of humans into his army as a severe transgression, the Librarian imprisoned the Didact on Requiem and sealed off the shield world while taking control of the mechanical Promethean forces stationed there, tasking them with preventing outsiders from awakening the Didact.
In July 2557, over four and a half years after the end of the Human-Covenant War, John-117 and Cortana, drifting aboard the wreckage of the UNSC Forward Unto Dawn, came across Requiem. They and a Covenant remnant force were forcibly pulled into Requiem and crashed on the surface, and were soon after engaged by the Promethean constructs inhabiting the shield world. After John-117 accidentally awoke the Didact, the latter took control of the Prometheans. Bent on preventing humanity's ascendance to the Mantle in the Forerunners' place, the Didact went to war with humanity, trying to use the Composer to neutralize his ancient enemies forever. The Prometheans and Covenant remnant aided in this plan, but with the help of the AI Cortana, the Master Chief defeated the Didact and destroyed the Composer and his ship Mantle's Approach with a HAVOK tactical nuclear weapon. However, the Promethean constructs continued to oppose the UNSC forces when the UNSC Infinity returned to Requiem in February 2558.
- Prometheans are color-coded based on the individual in command of them at the time; blue is used to represent the Librarian, while the Didact is represented by orange. Prometheans with blue lights only appear in the level Forerunner, until the Didact takes control of them in the final cutscene. Despite this, there is no in-game difference between the way the orange or blue Prometheans behave.
- The name "Promethean" was probably inspired by the Titan Prometheus in Greek mythology, who gave the gift of fire to mankind. However, there is no in-universe relation between the names, as the Forerunners predated the Greeks by well over 100,000 years.
- "Promethean" was one of the names Doctor Halsey considered for the SPARTAN-II Program.
John-117 facing the Didact's Cryptum.
 List of appearances
- Halo: Cryptum (First appearance)
- Halo: Combat Evolved Anniversary
- Terminals (Mentioned only)
- Halo: Primordium
- Halo 4
- Halo: Silentium
- ^ Halo: Combat Evolved Anniversary - Terminal 10
- ^ Halo: Cryptum, page 54
- ^ Halo Waypoint: Halo 4 Interactive Guide
- ^ a b c d e Halo 4, Terminals
- ^ a b Halo 4 Official Site, Characters
- ^ Halo: Cryptum, page 65
- ^ Halo: Cryptum, page 77
- ^ Halo: Cryptum, page 162
- ^ Halo: Cryptum, page 174
- ^ Halo: Cryptum, page 95
- ^ GameInformer, October 2012 edition (digital content)
- ^ Halo: Cryptum, page 238-239
- ^ Halo: Primordium, page 336-339
- ^ Halo 4, Spartan Ops
- ^ Dr. Halsey's personal journal
- ^ Xbox.com: Xbox Press Center - Halo 4 - Artwork (Halo 4 Key Art - Cryptum_Vertical)