From Halopedia, the Halo wiki
A Soldier, occasionally referred to as a Promethean Soldier due to the constructs' operational origins, is a class of the armiger developed and primarily utilized by the Forerunner Prometheans. Classified as bipedal combat platforms, Soldiers were deployed during the human-Forerunner wars and the Forerunners' war against the Flood.
Unlike the Promethean Knights, which are controlled by the composed essences of formerly living beings, Soldiers are purely artificial intelligence-driven. Soldiers have a distinctly humanoid appearance in comparison to other Promethean constructs and Sentinels; they have one set of arms with small, five-fingered hands. Their main locomotion is provided by a pair of long, thin legs designed for agility and speed. Soldiers are covered in patterns of light and have a fire-like glow inside their heads. In addition, they are capable of slipspace translocation. Unlike the other Promethean units, Promethean Soldiers are also capable of speech. The Soldiers encountered in the modern era are known to taunt their human opponents in English.
During the Human-Forerunner war, the Ur-Didact deployed Armigers. Due to their bipedal form and agility, the Armigers proved incredibly useful for raiding ancient human warships, particularly when infiltrating the vessels' confined spaces.
Following the conflict, the Didact was forced into exile by the ecumene Council, and his rate was diminished. When the Flood eventually returned, the ecumene found themselves dangerously unprepared, and so the Master Builder Faber recommissioned the production of Armigers to combat the Flood and to compensate for the dwindling number of Warrior-Servants.
While most Soldiers were expended during the Forerunner-Flood war, some were tasked with guarding key Forerunner sites in the event the Halo Array was fired. The UNSC first encountered these Soldiers in 2558 under control of Cortana and her faction, the Created, and they have since been integrated into the Spartan-IV War Games simulations aboard the UNSC Infinity.
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