Ancilla

Ancilla was a Forerunner term for an AI construct. They came in several varieties, each designed for different purposes and possessing differing capabilities. Although the term was often used to refer to all Forerunner AI, ancillas and monitors were sometimes referenced as distinct categories, monitors being defined by their floating robotic shells whereas ancillas, in general, were disembodied.

Background
Ancillas were ubiquitous in Forerunner society, and were housed within personal shells like those of the monitors, as well as personal armor, ships, buildings, and various forms of machinery. The most powerful ancillas, next to the Contender-class, were the Metarch-class ancillas. Ancillas possessed varying personalities, often approximating that of a Forerunner. Some ancillas designed to interface with Forerunners typically represented themselves via avatars similar to those used by human AIs. Not all ancillas assumed visible form, such as those that operated within a metarchy; a vast network of ancillas coordinated by a metarch.

Ancillas were also stored within a Forerunner's personal armor and could be accessed by the user at will for information via a form of neural link. Most personal ancillas assumed the form of a blue female Forerunner, manifesting itself in the "back of the wearer's thoughts". An ancilla's appearance would be modeled according to the species of the individual wearing the armor; for example, when Chakas and Riser received suits of Forerunner armor, their ancillas appeared as a female hamanune and chamanune, respectively.

For a Manipular, a personal ancilla made itself easily visible and readily accessible to provide guidance and education. Once Forerunners mutated to first-form, accessing the armor's ancilla appeared to require more effort, as it was expected that a mature Forerunner did not require as much attention as a Manipular; this also allowed the ancilla to divert more of its processing power to other tasks. Ancillas also helped Forerunners access the Domain after mutation.

The Forerunners viewed ancillas as little more than tools and programmed them to not only obediently perform their designated tasks, but, at least in some cases, also enjoy their servitude. The notion of an ancilla rebelling against its masters was virtually unprecedented, although this changed with the emergence of the Flood's logic plague which could effectively infect and convert Forerunner AIs.

For military purposes, Forerunners used software known as AI suppressors to disable ancillas used by hostile forces.

Varieties

 * Monitor
 * Metarch
 * Contender-class artificial intelligence

Trivia

 * Bornstellar's relationship with the Librarian's ancilla in Halo: Cryptum is similar to that of John-117 and Cortana. Like Cortana, Bornstellar describes his ancilla as a "blue female figure in the back of his mind" who can be stored within his body armor, and relies upon her for guidance and help in many situations.
 * Ancilla's modern definition is "an aid to achieving or mastering something difficult", or put simply, an accessory or auxiliary. The original Latin meaning of "ancilla" is 'female servant/slave' or 'maid'.

List of appearances

 * Halo: Combat Evolved
 * Halo: Combat Evolved Anniversary
 * Terminals
 * Halo: The Flood (2010)
 * Halo 2
 * Halo: Ghosts of Onyx
 * Halo 3
 * Halo: Contact Harvest
 * Halo Wars
 * Halo: Helljumper
 * Halo Legends
 * Origins
 * Halo: Blood Line
 * Halo: Cryptum
 * Halo: Primordium
 * Halo 4
 * Halo: Silentium
 * Halo: Rebirth