Game of Thrones was controversial for a number of reasons, not least of all the removal of a certain major character from the books: Lady Stoneheart. The omission of the undead version of Catelyn Stark was, unsurprisingly, met with antagonism from fans of George R.R. Martin's books.
David Benioff and D.B. Weiss have previously discussed the decision, but never in quite this much detail. For a new behind-the-scenes book, Fire Cannot Kill a Dragon, the showrunners revealed why they decided not to include Lady Stoneheart, and it has a lot to do with Martin's still-secret plans for the character.
“Part of the reason we didn’t want to put it in had to do with things coming up in George’s books that we don’t want to spoil [by discussing them],” Benioff said, as revealed by EW. Most readers presume this has something to do with Jaime Lannister or Brienne's storyline, though nothing's known for certain.
That wasn't the only reason for Stoneheart's no-show. They were also fearful that bringing back Catelyn would take away from Jon Snow eventually being resurrected in future seasons. "We knew we had Jon Snow’s resurrection coming up,” Benioff said. “Too many resurrections start to diminish the impact of characters dying. We wanted to keep our powder dry for that.”
There was also the fact that the Red Wedding was so impactful, that bringing back Catelyn could have taken away from just how major that moment was. “Catelyn’s last moment was so fantastic, and Michelle [Fairley] is such a great actress, to bring her back as a zombie who doesn’t speak felt like diminishing returns,” Benioff said.
Despite this, Martin believes the character should have been included in the show, saying: “Lady Stoneheart has a role in the books. Whether it’s sufficient or interesting enough. I think it is or I wouldn’t have put her in. One of the things I wanted to show with her is that the death she suffered changes you.” That comment probably won't cause a stir in the fandom...