Monitors : 343 Guilty Spark and 2401 Penitent Tangent
The floating blue orb better known as 343 Guilty Spark is the AI Monitor, caretaker, and historian apparently left to keep watch over Alpha Halo Installation 04 and its contents when the Forerunner departed. In a similar fashion as most human AIs, he has several blocks on him which do not allow certain behaviour- for example, he cannot retrieve the Index from the Library or unify it with the Core. He needs the Master Chief, Mobuto, Miranda Keyes, Sgt. Johnson, or another being fitting the requirements of "Reclaimer" (seemingly just a member of the Human race) to do this for him.
343 is quirky and good humoured, though at the same time detached and by-the-book. Protocol is king; the slight emotion shown for those who die along the way seems only to truly mourn the inconvenience of finding another to assist him. "Having had considerable time" to check and recheck the systems of Halo in his masters' absence, the possibility has grown exponentially that his isolation has given more than slight opportunity for an unusual quirkiness to bubble to the surface.
Free from his commitments on Installation 04 (and floating aimlessly in space), the Monitor was happily retrieved by a group of "Heretics": an Elite and his followers preaching open rebellion against the Prophets and their lies of the supposed salvation The Great Journey has to offer. With the slaying of the Heretic leader, 343 was summarily captured and interrogated by the Prophets (referred to as "The Oracle") before eventually falling in alongside the newly united forces of the Arbiter, Miranda Keyes, and Sgt. Johnson. Now if everyone could just stop fighting long enough to hear what he's got to say...
2401 Penitent Tangent is the red-tinged Monitor left with the similar charge of maintaining Delta Halo 05. Little is known about him, or how long he had been in the custody of Gravemind, but he appears to be no less concerned with the strict adherence to protocol. Although, after all these years, he seems to be a tad less worse for wear emotionally than 343. His present fate is unknown.
Hee Hee Hee, je suis un geni ! xD