The Librarian

Well, apparently shes the most beautiful Forerunner ever, and the mother of Humankind. She was the companion of the Didact, but he went insane and killed everyone in the Galaxy, so she went off him. Luckily she managed to save specimens of every single species in the Galaxy, you know, just in case.

She turned Johnny into an even more kickass supersoldier, and made him immune to the Composer.