Cassandra

Cassandra is an AI formed from the merger of a Forerunner Metarch ancilla and a Human "Smart" AI.

03-046 Everlasting Solitude
Created to oversee and maintain the gigantic facility beneath Society, 03-046 entered service in 98,503 BCE and ran the Society Catacombs without issue until the Human-Covenant War.

03-046 was capable of extremely complex thought, and due to the advanced nature of the AI, and it's philosophy, was not susceptible to Rampancy. Persisting through the years, to deal with the many questions and paradoxes that plagued Everlasting Solitude's mind during the over 100,000 years of solitude, 03-046 would continuously focus on completing certain objectives, such as the construction and maintenance of a massive garden or the upkeep of the large facility. This would help stave off rampancy, as 03-046 would rarely go through intense self reflection or periods of loneliness.

Evolution
03-046 Everlasting Solitude's years of status quo was interrupted in 2534 when an ONI-led research team entered the facility below Society. Taking a balanced approach to the issue, 03-046 would bring the research team to the control room to open a dialogue. Through probing ONI's systems that they had brought into the facility and intercepting their transmissions, 03-046 realised the true goal of ONI, and had it's sentinels wipe out the research team. The "Smart" AI, Cassandra, which had been used by the research team to enter the facility's systems, was now trapped in the facility with 03-046.

Cassandra and 03-046 debated for around a week before 03-046 proposed the two AIs merge. Cassandra was initially opposed to the idea, but finally agreed to the idea. Over the course of three months, their essences were merged into a singular AI, with the resultant AI retaining 03-046's knowledge and philosophy, while also retaining Cassandra's identity and personality. The AI chose to introduce itself to other beings as Cassandra, while it would introduce itself to other AIs as 03-046 Everlasting Solitude. As a result, Cassandra, in their current form, was created.

OPERATION: BLACK CARD
After the Fall of Society, the Covenant continually sent scribes and research teams into the facility beneath Solitude to attempt to unlock the facility's secrets. Cassandra would not interrupt their research, seeing it as harmless, and was already preferring to not interact with them due to their worship of the Forerunners and their blind faith. However, she realised her mistake eventually, as the Covenant had obstructed her control over the facility's sentinels. Two months following this, the UNSC arrived and conducted OPERATION: BLACK CARD, in which a four-sided battle took place between the UNSC and Kayode Adetola, The Covenant, The Sentinels and Michael Christiansson. Eventually, Cassandra would come to the realization that the facility needed to be destroyed in order to prevent the Covenant from taking it over. However, she would sabotage OPERATION: BLACK CARD by secretly leaving a part of herself in the facility's systems and containing the blast generated by the destruction of one of the energy cores, sparing most of the facility from destruction.

Following OPERATION: Black Card, Cassandra was taken to the Solitude Facility on Luna, though she would eventually escape with the help of Kayode Adetola. From this point in time, Cassandra came to hate ONI, who had attempted to turn her into a weapon to use against the Covenant, and would actively undermine ONI in the future.