Halo TV series recasts Cortana with the voice actor from the games
Natascha McElhone was signed to portray Cortana and Dr. Catherine Halsey, but has run into scheduling difficulties.
The Halo TV series has a new Cortana, and it's actually the old Cortana: An IGN report says that Natascha McElhone, who was originally cast as the blue-hued AI as well as its creator Dr. Catherine Halsey, cannot fill both roles because of scheduling conflicts caused by the COVID-19 pandemic. So Showtime has enlisted Jen Taylor to do the job instead.
Taylor, as a trip to IMDB will tell you, is a very experienced voice actor, with a career stretching back more than two decades—including (this is the important bit) the role of Cortana in every main Halo game from Combat Evolved to the upcoming Halo: Infinite. (And also Forza Horizon 4, for some reason.) She knows a thing or two about the character, in other words—to the point that you might wonder why she wasn't cast in the role in the first place.
Other notable voices Taylor has provided over the years include Cate Archer in No One Lives Forever 2 and Contract Jack, Jessica Cannon in Sin Episodes, Zoey in Left 4 Dead, Atomic Wonder Woman in Infinite Crisis, and Princess Peach in a whole big pile of Mario games.
McElhone will continue to portray Halsey (who, in an amusing little twist, is also voiced by Taylor in the Halo games) in the television series. It's not known at this point whether Taylor will appear in the show as Cortana, or simply provide the voice for a CGI character.
Showtime's Halo series was announced in 2013 but production didn't get underway in earnest until 2018. Pablo Schreiber of The Wire and Orange is the New Black was unveiled as the show's Master Chief in 2019, while the rest of the cast was revealed later that same year. An official air date still hasn't been announced, but it's expected to arrive sometime in the first quarter of 2021.