Benioff and Weiss recast two starring roles between the making of the first and second pilots: Jennifer Ehle was replaced by Michelle Fairley as Catelyn Stark, since Ehle didn’t want to move to Northern Ireland, and Tamzin Merchant was replaced by Emilia Clarke as Daenerys Targaryen, because Merchant’s scenes with Jason Momoa (Khal Drogo) weren’t quite right.
The unaired pilot was apparently super ambiguous about the nature of Jaime and Cersei’s relationship, and audiences missed the fact that they’re siblings. But the showrunners were actually more faithful to a key sequence from George R. R. Martin’s book during their initial attempt: Daenerys and Drogo’s wedding night, rewritten to be a rape scene in the second pilot, was first shot as a consensual encounter, just like it is in the source material.
Some production elements were changed as well, from the timing of scenes (the wedding was originally filmed at night, and “quite a lot of money had been spent on seeing absolutely fuck-all”) to the costuming (apparently, Cersei looked like a “medieval Dolly Parton” in her first incarnation).
