The Halo television series coming to Showtime has found its Cortana. Natascha McElhone will take on the role of the advanced artificial intelligence, who often serves as an advisor to series protagonist Master Chief.

McElhone is perhaps best known for her role as Karen on another Showtime series, Californication. McElhone will pull double acting duty on Halo; she’ll also play Dr. Catherine Halsey, the creator of the Spartan super soldier project, whose brain was used as the basis for Cortana’s creation.

Related Halo TV series casts its Master Chief

Also joining the cast of Halo is actor Bokeem Woodbine (Fargo, Spider-Man: Homecoming), who will play Soren-066, described as a “morally complex privateer at the fringes of human civilization whose fate will bring him into conflict with his former military masters and his old friend, the Master Chief.” Soren-066 appeared briefly in Halo canon in the short story “Pariah” from the Halo: Evolutions collection.

Showtime also announced that actor Shabana Azmi will play Admiral Margaret Parangosky, the head of the Office of Naval Intelligence.

The Halo TV series will also introduce three original Spartans, played by actors Bentley Kalu (Avengers: Age of Ultron), Natasha Culzac (The Witcher), and Kate Kennedy (Catastrophe). From Showtime:

The series will also introduce three all-new characters to the Halo universe. British actor Kalu will play Spartan Vannak-134, a cybernetically augmented supersoldier conscripted at childhood who serves as the defacto deputy to the Master Chief. British actress Culzac will star in the role of Spartan Riz-028 – a focused, professional and deadly, cybernetically enhanced killing machine. Kennedy stars as Spartan Kai-125, an all-new courageous, curious and deadly Spartan supersoldier. Yerin Ha was previously announced playing the new character Kwan Ha, a shrewd, audacious 16-year-old from the Outer Colonies who meets Master Chief at a fateful time for them both.

In April, Showtime announced that Pablo Schreiber will play the lead role of Master Chief in Halo. Showtime is producing the series with 343 Industries and Steven Spielberg’s Amblin Television. Production is slated to being this fall in Budapest, Hungary.

Halo will be executive-produced by Kyle Killen (Awake, Lone Star) and Steven Kane (The Last Ship, The Closer), who will also serve as co-showrunners. Otto Bathurst (Black Mirror, Robin Hood) will direct the pilot and multiple episodes of the nine-episode series.