Board Thread:Questions and Answers/@comment-124.240.187.87-20150724111647/@comment-1031724-20170831072857

Currently it's both Cersei and the Night King. The Night King is the bigger and more immediate threat now but Cersei is waiting on the sidelines ready to kill whichever side wins the war, and she's queen of the Seven Kingdoms, to be the main enemy if the White Walkers are defeated (and that's a big IF).

There isn't just one. I'd say the main antagonists of the series are Cersei (Seasons 1 and 7), Joffrey (Seasons 1-3), Tywin (Seasons 2-4), Mance Rayder (Seasons 2-4), Melisandre (Seasons 2-5, some would count Stannis as well coz he made the choice to listen to his devil rather than his angel), Theon Greyjoy (Season 2), Balon Greyjoy (Bigger Bad of Season 2 behind Theon), Ramsay Bolton (Seasons 5 and 6), Roose Bolton (Season 5), the High Sparrow (Seasons 5 and 6), the Slave Masters (Seasons 5 and 6), and of course, the Night King (Seasons 5-7), on account of being the most prominent villains with the greatest antagonistic presence. Viserys and Littlefinger could count as secondary, for Seasons 1 and 7, respectively.

But, closest to a "Sauron" of the series is the Night King. He is the ultimate threat.