Cortana is a fictional artificially intelligent (AI) character in the Halo video game series. Voiced by Jen Taylor, she appears in Halo: Combat Evolved and its sequels, Halo 2, Halo 3 and Halo 4, in the prequel and epilogue of Halo: Reach, and 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.
Cortana's original design was based on the Egyptian queen Nefertiti; the character's holographic representation always takes the form of a woman. Taylor, despite her extensive voice acting for video games, is not a gamer; she described portraying Cortana as challenging, due to the character's lack of a physical form. Bungie first introduced Cortana—and Halo—through the Cortana Letters, cryptic emails sent during Combat Evolved's production in 1999. Since then, the character has been used extensively to advertise the series. Cortana has been recognized for her sex appeal, believability and character depth.