This list could go on forever, TBH.
Mahershala Ali as former Daenerys stan Xaro Xhoan Daxo.
Back in January, the Oscar-winning star told Jimmy Kimmel that he felt like he was “too stiff” during one of his auditions for Thrones because of the awkward, backless stool he was sitting on. All these years later, casting director Nina Gold admitted to Vanity Fair, “Wow, how could I have ever turned down Mahershala Ali?”
Netflix / HBO
Gillian Anderson as (maybe???) mother-of-the-year Cersei Lannister.
Although Anderson and Gold have not elaborated on which character Anderson had been considered for on Thrones, many fans have speculated it was for the role of Cersei Lannister. Gold told Vanity Fair that she is a favorite actor of hers. And in 2013, Anderson told The Daily Mail, “My 18-year-old cannot believe that I would turn down Game of Thrones or Downton—things she loves to watch.”
NBC / HBO
Sam Heughan as hot king Renly Baratheon.
In an interview with Vulture a while back, the Outlander star explained how he auditioned “loads of times” for Thrones including for the roles of Renly, Loras, and even some of the Night's Watch characters.
Starz / HBO
Tamzin Merchant as perfect being Daenerys Targaryen.
Merchant was another recast after the troublesome original pilot was filmed. According to Time, George R. R. Martin loved her performance as fifth wife of Henry VIII, Catherine Howard on Showtime's The Tudors as well as her initial reading as Daenerys. But no one really knows why she was recast!
Starz / HBO