Stratus

Stratus
Stratus was the AI of the Reilly's Rangers and of Regan in specific. He was created by Dr. Harry West in 2549, the same one who worked on Regan. He served in many battles and was a very important unknown figure in the UNSC Air Force. With his assistance, Reilly's Rangers helped many and saved many. Stratus died 2557 of AI aging.

Battles
Stratus served in 53 battles and skirmishes, including the Fall of Reach, the Battle of New Mombassa, and the escort of John S-117 on Installation 04. He was also in many skirmishes later on in his career under a different affiliation, an Agent and his Spartan SIV team, although it's unknown. Fireteam Tzu matches the description, so it's assumed it's that group, although, there are statements from ONI Admiral Dan Willis saying there was no AI on that team from his knowledge. Other than that, his service details were a mystery.

Personality
Stratus was a snarky, sarcastic, obnoxious, and almost rude individual who treated his team like crap when they failed a skirmish, and he tried his best to make the battle a win. Saying that, he was a perfectionist, and made everything the way he saw fit. Stratus was also deeply caring, an irregular feature in an AI, and whenever he saw any troops dying he'd tell the team to save that person, and attended memorials for battles and his squad when they died.