Librarian

The Librarian was a Forerunner being.

He/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 He/she was left on what is more likely Earth soon before the original activation of the Halo ringworlds, unable to leave the planet due because of the severity of the Flood/Forerunner war.

His/her lover was the Didact, believed commander of the Forerunner military.