Then God help you, because if your plan fails, no one else will have the power to do so.
Wellsley was a 4th generation, Class-C Military AI who helped Major Antonio Silva and First Lieutenant Melissa McKay setup and operate the Alpha Base on Installation 04. He was consumed in the destruction of the Truth and Reconciliation.
As with all AIs, Wellsley had the ability to choose his appearance. He chose to appear as a stern-looking man with long hair, a prominent nose, and a collared coat, and so resembled his namesake, Arthur Wellesley, the Duke of Wellington. Wellsley was created to act as a military assistant. He often referred to his victories as though he were the actual Duke and not an artificial re-creation, which annoyed many of his acquaintances.
It is possible, though unconfirmed, that he was the other A.I for the UNSC Pillar of Autumn. Lieutenant Hikowa mentioned Wellsley as being for "point defense." A factor against this would be that he was already in Major Silva's HEV (Human Entry Vehicle) when he arrived. It is also possible that "his" purpose as a second AI would be to guide Marine Forces whilst Cortana would guide the Spartans and fighter craft.
Like the earlier AI FitzGibbon, Wellsley took the form of an 18th-century officer in the British Army.
Wellsley picked out a butte on the surface of Alpha Halo to Major Silva to act as an effective home base for the scattered UNSC forces on Halo. Later he also warned Silva about a Covenant motorized counterattack, which he compared to the French cavalry charge at Waterloo, much to Silva's annoyance. After Alpha Base was secured, he rapidly took command of its anti-air defenses when the Covenant raided it in search of John-117, and managed to shoot down one of the six approaching Covenant controlled dropships.
When the surviving Marines and ODSTs captured the Truth and Reconciliation, Wellsley sided with First Lieutenant McKay and attempted to convince Silva not to leave until they were sure that every last Flood on the ship was exterminated. When McKay cut the communications to the engines, the Covenant ship lost control and crashed on Halo. Wellsley was presumed lost in the crash, as was almost the entire remaining UNSC presence on Halo. He was fully aware of McKay's actions and just before the ship crashed, he told Silva that if he could be proud of one thing, it was that he had taught McKay well.