12 Biggest Unanswered Game Of Thrones Mysteries
8. Howland Reed
Howland Reed has appeared on the TV show, courtesy of the Tower of Joy flashback in Season 6, but the character is yet to appear in the current timeline in either the show or the books - and it doesn't look like happening anytime, well, ever on TV.
Despite the general lack of him, the Crannogman is a crucial figure to the events of the series: he's the only person still alive who was at the Tower of Joy and knows the truth about R+L=J.
Obviously Bran's powers make that less of an issue, but he could still be important in convincing the realm of the validity of the claims. So where is he? Why has he never appeared? He sent his kids to Bran's side, but for reasons we don't know he hasn't left his home of Greywater Watch since the end of Robert's Rebellion.
Curiously, George R.R. Martin has said (a long time ago) that Howland would appear eventually, but whether that's a flashback or actually in the present remains to be seen.