Cortana is a fictional synthetic intelligence character in the Halo video game series. Voiced by Jen Taylor, she appears in and its sequels, Halo 2, Halo 3, Halo 4 and Halo 5: Guardians. She also appears in a cutscene and the epilogue of the prequel , as well as in several of the franchise's novels and comics. During gameplay, Cortana provides backstory and tactical information to the player, who assumes the role of Master Chief Petty Officer John-117. In the story, she is instrumental in preventing the activation of the Halo installations, which would have destroyed all sentient life in the galaxy.