The Boltons were among the last lords to submit to the kings of the Stark line. Before that time they fought with implacable ferocity against the Kings of Winter as recently as the time not long after Bael the Bard’s death at the Frozen Ford, when a Bolton lord was said to have slain a Stark and wore his skin as a cloak. It is also said that there is still a room in the Dreadfort where the skins of their enemies are displayed.
The current lord of the house is Roose Bolton. After the death of his young son Domeric, his heir is his bastard son Ramsay Snow.
Lord Roose was given command of the Robb Stark’s infantry and was defeated by Tywin Lannister at the Green Fork but was able to retreat in good order. He has since married one of Lord Frey’s daughters, and with the help of the Brave Companions has taken Harrenhal from the Lannisters after Lord Tywin marched out with all his army but a small garrison.
Ramsay Snow was believed killed by Ser Rodrik Cassel after he had committed gross crimes, including the forced wedding and bedding of Lady Hornwood, and then letting her starve to death, so that he could lay claim to the Hornwood lands. It was later revealed that he survived by impersonating a cruel servant, Reek. He brought a garrison from the Dreadfort to destroy the host Ser Rodrik had raised against Prince Theon Greyjoy at Winterfell, and then turned on the ironmen.
Roose Bolton eventually betrayed Robb Stark at the Red Wedding, where King Robb, Lady Catelyn, and many others besides were slaughtered in a bloodbath. Lord Roose was rewarded by being made Warden of the North and Ramsay Snow was legitimized. Ramsay proceeds to march against the ironborn, bringing in tow his new Reek—the horribly maimed and tortured Theon Greyjoy—to do his bidding. Slaughtering the ironmen at Moat Cailin, Ramsay meets with his father, who does not particularly care for his only son and heir. Lord Roose proceeds to raise an alliance of northern houses aimed at defeating Stannis Baratheon once and for all, leading his forces to be in Winterfell where his son weds “Arya Stark”—in truth Jeyne Poole—in a ceremony to seal their claim to the rule of the North. However, Stannis’s forces are nearby at this time, and as tensions mount within the castle walls Lord Bolton orders the Freys and Manderlys to ride against the enemies outside their walls.