Promethean

"They're Forerunner robots. Hard light in battle armor. Ruthless. Brutal. What can they offer us? Nothing but trouble, doctor. They're simply killing machines."

- Gabriel Thorne

The Prometheans were the highest and most respected group of Warrior-Servants in the Forerunner Ecumene. The Didact and Confirmer were Prometheans. Physically, Prometheans were the highest form a Warrior-Servant could mutate to, standing around four meters tall and between 800 and 1,000 kilograms in weight. They were heavily muscled, their hands capable of easily crushing a human skull.

History
Following the Human-Forerunner wars and the discovery of the Flood, the Prometheans stood in opposition to the radical faction of Builders who proposed the construction of the Halo Array. They lost the political battle, and were subsequently removed from the Council. The Prometheans were responsible for creating "Warrior Keeps" known as Cryptums. In order to counter the flood, the first Prometheans were volunteers from the Forerunner Warrior-Servant caste, however requiring more numbers to defeat the Flood, the Diadact took devolved Humans and made them into the next generation of Prometheans.

Halo 4
The main enemies in Halo 4, introduced as a new class of opponents are the Promethean Knights, Crawlers, Watchers and a Forerunner Promethean known as The Didact.

The Librarian reveals to the Master Chief that some of the Prometheans are humans, transformed by the Didact by means of a device known as "The Composer". When the Encumene discovered the Didact's plan to turn all of humanity into Prometheans to gain immunity to the Flood, they removed The Composer from the Didact (hiding it on Installation 03) and imprisoning him in Requiem. Through her manipulation of humanity's genes, the Librarian was able to hide an immunity to the Promethean transformation in the Master Chief's genes.

Trivia

 * 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 pre-dated the Greeks by well over 100,000 years.
 * Even though the Librarian said that the Prometheans were once human, a terminal in Halo 4 reveals that the Didact's army had willingly changed themselves into the Prometheans. Therefore it can be assumed that some of the Prometheans (Halo 4 enemies) were human and others were Prometheans (Forerunner Warrior-Servants)
 * Upon first encountering the Prometheans in Halo 4, they all have blue coloring on their bodies. This is changed to orange by the Didact after being freed from his prison, as the Didact reclaims control over his army. The coloring likely represents who is ordering them or commanding them.

List of appearances

 * Halo: Cryptum
 * Halo: Combat Evolved Anniversary
 * Halo 4