George R. R. Martin has done something new in fantasy. He has created a world in shades of gray. This is in contrast to the modern template of J. R. R. Tolkien’s The Lord of the Rings, where what is good and what is evil were as clear and distinct as black and white. In addition, A Song of Ice and Fire transcended fantasy’s traditional appeal to adolescent males. This latter tendency is pretty evident in Robert Jordan’s The Wheel of Time, which was simply not moving beyond its juvenile origins by book seven or eight, when I gave up (I was moving beyond my juvenile origins by that point). It isn’t as if the Jordan-style, geared toward adolescent male virgins, can’t be done well. I’d argue that Brandon Sanderson pulls this off very competently.
One of the aspects of A Song of Ice and Fire in the books is there isn’t a Dark Lord who is the literal personification of evil. No Sauron. Even the primary antagonists become less dark with deeper exploration, and their motivations are often complex, and comprehensible in their own way.
But there is a major exception to this: Ramsay Snow and House Bolton. The Boltons are the great rivals of the Starks in the North, and before they were vassals they were kings. And they are evil in a straightforward sense without nuance. One stupid “fan theory” (these are the television show watchers) even posited that Roose Bolton was an immortal vampire.
Though Martin is careful to suggest that people should not take the antiquity of the dynasties in A Song of Ice and Fire literally, it is clear that the Bolton’s are not parvenus. Their lineage is old, and it has persisted. And yet the Boltons which are highlighted are basically without any redeeming qualities over their history. Ramsay Snow is basically the protagonist of a snuff film come alive.
When it comes to mining history perhaps the best analog to the Boltons were the Assyrians. Like the Boltons they flayed their enemies alive. The Assyrians also famously were totally destroyed by their enemies because of the ill-will their cruelty in conquest generated. Martin is a student of history, and there is no way that a lineage of such unmitigated evil could persist down the centuries. The Boltons exist as witness to the long tradition of fantasy antagonists which readers love to hate.