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 defense of the city by local militia, police, and UNSC Marines.

In his attempts to find Sadie, Commissioner Kinsler shut down the Superintendent, in order to prevent it from helping her. 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 by 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 began to merge the badly damaged Vergil with itself, a process that was complete just as it was discovered by Captain Veronica Dare and the Rookie. Early in this process, Vergil, with the Huragok controlling it, helped to free Sadie from Kinsler by opening the doors of his private train and letting the mob of refugees rip Kinsler apart.

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. A month later, Sergeant Major Johnson has a talk with Vergil, who was in the process of accessing the Covenant battle net, about the information it has. Vergil agrees to share any information it has with the Sergeant and lights his cigar as a friendly gesture.

Trivia

 * The name Vergil itself may be a reference to the Divine Comedy, specifically to Virgil, 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.
 * Like the other Engineers found in the game and in spite of its lack of armor, Vergil still has shields to protect himself, and also is able to grant close friendly units shields, including the player. However, the player has no shield monitor and can go down in a heartbeat on Legendary.