Librarian

The Librarian was a Forerunner being.

she sought to document and index all sentient beings of the Milky Way galaxy and protect them from the Flood by sending them to the shelter of the Ark. The Librarian cut herself off from the Flood/Forerunner conflict by deactivating the portal leading to Instillation 00 (The Ark), leaving her isolated on Earth.

her lover was the Didact, commander of the Forerunner military.