The Mastermind

"The Mastermind" was a fragment of abstracted personality. It was destroyed by Flood-infected battleship that had destroyed the Forerunner vessel that was ferrying it to the Ark.

Nothing is currently known about "The Mastermind", other than it's translated title. It's title, as well as prior knowledge on Forerunner Ancilla suggests that this core may have coordinated and planned Flood assaults in their effort to assimilate the native fauna of the Milky Way Galaxy, perhaps even the infamous assault on the Maginot Sphere.

History
In order to prevent Mendicant Bias from subverting or harming him, Offensive Bias had shattered of Mendicant Bias into its component sections and scattered them throughout the few remaining ships of his fleet for transport to Installation 00, where he would study the fallen AI construct. Much of his fleet was destroyed or ravaged by the Flood. The "The Mastermind" was destroyed in this manner.