Araqiel

As Colonel James Ackerson's private A.I., Araquiel was tasked to spy on Dr. Catherine Halsey and her research. His appearance is that of an elongated skull with long, demon-like horns, fire-filled eyes and jagged teeth. His voice is a low bestial growl or rumble containing a trace of far-off thunder. He was left at CASTLE Base in 2552 during The Battle of Reach. He threatened Dr. Halsey and Kalmiya after he attempted to stop her from breaking into Ackerson's private data files during the Covenant assault on the planet Reach. He even went so far as to threaten to fill Halsey's office with fatal levels of Narcozine Gas or to pressurize her office and cause pulmonary edema.

Dr. Halsey responded by activating the fail-safe in his Riemann Matrix, effectively destroying him.

Trivia
The name comes from that of a Fallen Angel described in the Book of Enoch, justifying his appearance.