Hannah Waddingham has joined the cast of Syfy’s “Krypton.”

According to Deadline, Waddingham will play the recurring role of Jax-Ur. Formerly one of Krypton’s greatest scientists with deep ties to Krypton’s past, Jax-Ur is now determined to bring radical change to Krypton as leader of the underground terrorist organization, Black Zero.

In DC mythology, Jax-Ur has traditionally been male. Jax-Ur was most recently played by Mackenzie Gray in the 2013 film “Man of Steel.” Ron Perlman also voiced the character in “Superman: The Animated Series,” which aired from 1996 to 2000. Waddingham will be the first female to play the character.

Shortly after her casting was announced, Waddingham took to Twitter to share the news with her fans. Check out her tweets below:

Waddingham is best known for her role as Septa Unella on HBO”s “Game of Thrones.” The English actress also recurred as Magdalena Syfy’s “12 Monkeys.” On the film side, she appeared in the 2012 musical drama “Les Miserables” and in the 2008 British comedy movie “How to Lose Friends & Alienate People.” Waddingham will also be seen next in the British thriller “Water Ridge,” which opens in theaters in the UK on March 19.

Set two generations before the destruction of Superman’s home planet, “Krypton” follows the Man of Steel’s legendary grandfather Seg-El (Cameron Cuffe), whose family was ostracized and shamed after it failed to end tyranny. As he fights to redeem House of El’s honor, Seg encounters Earthly time-traveler Adam Strange (Shaun Sipos) who tells him that he’s under the clock to save his beloved world from chaos. “Someone from the future is coming to destroy Krypton,” Adam tells Seg in the trailer for the series. “Because where I’m from, your grandson becomes the greatest hero of the universe.”

In addition to Cuffe and Sipos, Waddingham also joins cast members Ian McElhinney as Seg’s grandfather Val-El; Georgina Campbell as Seg’s lover Lyta Zod; Elliot Cowan as Kandor’s Chief Magistrate Daron-Vex; Ann Ogbomo as Lyta’s mother Alura Zod; Rasmus Hardiker as Seg’s best friend Kem; Wallis Day as Daron’s daughter Nyssa-Vex; and Aaron Pierre as Dev-Em.

“Krypton” premieres on Wednesday, March 21 on Syfy.