Vergil

Originally, Vergil was a subroutine built into the larger Superintendent artificial intelligence, created by Dr. Endesha to look after his daughter, Sadie Endesha. Using the endless resources of New and Old Mombasa, Vergil performed its tasks without fault, although Sadie found it to be a little restrictive. When the Covenant attacked the area, Vergil was instrumental in Sadie's escape from harm in her struggle to reach her trapped father, commandeering numerous vehicles to assist her, as well as the defence of the city by local militia, police, and UNSC Marines.

In his attempts to find Sadie, Commissioner Kinsler shut down the Superintendent, hoping that it would lure her out of hiding. Eventually reactivated, Vergil had been badly damaged and was near to total system shutdown, saved only by the efforts of a renegade Covenant Huragok. Unwilling to continue as slaves to the Covenant, seven Huragok had made an attempt at escape. Six of them were destroyed during this attempt, giving their lives so that the seventh could flee, eventually, it made its way to the core of the Superintendent, working to repair it. As it worked, the Huragok managed to merge the badly damaged Vergil with itself, essentially becoming Vergil.

Later, the new Vergil would defect to the UNSC, allowing itself to be captured by Veronica Dare and her team of ODSTs, to give the UNSC vital information on the Covenant, and their intentions for New Mombasa. Later, after the credits, Sergeant Major Johnson has a talk with Vergil about the information he has. Vergil agrees to share any information he has with the Sergeant.

Trivia

 * In one of the final segments of Halo 3: ODST, one of Vergil's statements is "Warning: Hitchhikers may be escaping convicts." This is a reference to the final segment of Halo: Combat Evolved.
 * The name Vergil itself may be a reference to the Divine Comedy, specifically the name of the poet that guides fellow poet Dante through the nine circles of hell and purgatory, much in the same way the Rookie is guided through a metaphorical hell-on-earth, a destroyed New Mombasa.
 * He is the seventh surviving Engineer, an obvious seven reference.