It is not any of the humans. There are some characters that people love to hate, namely: Lord Tywin Lannister, Cersei Lannister, Joffrey Baratheon, Sandor Clegane, Gregor Clegane, Lord Walder Frey, the Boltons. You may like some characters more than others, and we’re rooting for the Starks for the most part, but George R. R. Martin is very careful not to let anyone be too good and even when we’re pretty sure someone is bad, he turns them around and has us rooting for them. All humans are shades of grey.
The title of the book series hints at what’s really going on in this world – A Song of Ice and Fire. We can clearly see 2 great forces at work, Ice and Fire. In the first book, the Others appear north of the Wall (forces of Ice and cold) while the dragons are born and Daenerys Targaryen discovers her power (forces of Fire and heat). Ice and Fire, both rising in power simultaneously.
The antagonist is…
The Great Other is the god of darkness, cold, and death in the faith of R’hllor. His true name is never spoken. He is considered the enemy of R’hllor, the Lord of Light. Followers of R’hllor believe that there are only two gods, R’hllor and the Great Other, who wage an eternal war over the fate of the world. All forces of darkness, cold, and death are believed to be only servants to the Great Other.
The Great Other somehow resides north of The Wall, in the Lands of Always Winter. He (or she?) created The Others (The White Walkers) who in turn create the zombies who plague the Wildlings and the Night’s Watch. The Great Other is probably responsible for the strange cycle of Winter that covers Westeros at random times.
R’hllor represents Fire, and his forces are not just the Red Priests like Melisandre. The dragons are also powered by R’hllor, the Targaryens contain the blood of dragons and probably the blood of R’hllor, while Varys & Illyrio Mopatis are somehow scheming for the return of Daenerys Targaryen and her dragons, probably to counter the rising threat of The Others north of the Wall.
The primary purpose of this post was to put forward a perspective so as to people stop branding every character as good or bad and enjoy the show/book better without having to search for the real antagonist. I hope I succeeded in doing so.
Thanks for reading!