Ancilla

Ancillas are a type of Forerunner artificial intelligence construct. They come in several varieties, each designed for different purposes and possessing differing capabilities. Known models include the Monitors, the Contender-class AIs, and the personal ancillas carried by most Forerunners.

Background
Ancillas can be stored within a Forerunner's body armor and can be accessed by the user at will. They can also be housed within personal shells like those of the Monitors, as well as ships, buildings, and various forms of machinery. They typically possess personalities approximating that of a Forerunner; in this respect, they are quite similar to human "Smart" AIs.

The most powerful ancillas, next to the Contender-class, are the Metarch-class ancillas which were used exclusively by the Forerunner Council. When a Forerunners is a Manipular, the ancilla tries harder to make itself more "visible" and readily accessible to the young Forerunner. But once the Forerunner mutates for the first time, the ancilla makes itself less visible so it can divert power to other tasks, making it much harder for the user to access them. It is also apparent that ancillas help Forerunners access the Domain after mutation.

Trivia

 * Bornstellar's relationship with the Librarian's ancilla is strikingly 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" is Latin for 'female servant' or 'maid'.

List of appearances

 * Halo: The Flood (2010)
 * The Forerunner Saga
 * Halo: Cryptum