I asked my halo friends about it, they said Cortana is a forerunner AI. She used to be the Librarians AI, she gave Bornstellar a clone of Cortana. Back on in Reach, if you played it, on The Package you see Halseys lab with Cortana, Halsey dug up Cortana as a Forerunner artifact, She had a blank image portayed. All AI's are based off people famous in the UNSC, Halsey was pretty famous at the time so she used some of her DNA to make Cortana project an image. Halsey wiped out most of her data, and put in UNSC data. Which this is after when the Gravemind made Cortana rampant and told her who she originally was, again, the Librarian and Bornstellar's AI.
The Librarian is dead in this game, she has been before. So I stand corrected on all my posts on Cortana.
Read the post above me.