Cortana is a fictional artificially intelligent character in the Halo video game series. Voiced by Jen Taylor, she appears in Halo: Combat Evolved and its sequels, Halo 2, Halo 3, Halo 4, Halo 5: Guardians and Halo Infinite. She also briefly appears in the prequel Halo: Reach, as well as in several of the franchise's novels, comics, and merchandise. During gameplay, Cortana provides backstory and tactical information to the player, who often 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.

Halo is a military science fiction media franchise, originally developed and created by Bungie and currently managed and developed by 343 Industries, part of Microsoft's Xbox Game Studios. The series launched in 2001 with the first-person shooter video game Halo: Combat Evolved and its tie-in novel, The Fall of Reach. The latest main game, Halo Infinite, was released in late 2021.