Ramsay Snow the bastard son of Lord Roose Bolton. He is known as the Bastard of Bolton and the Bastard of the Dreadfort. Ramsay considers himself a true Bolton despite his birth and is highly resentful of his baseborn status, referring to himself proudly as the trueborn scion of the Dreadfort and violently correcting those who refer to him otherwise.
Ramsay is the product of rape between Roose Bolton and a miller's wife. He spent most of his early life ignorant of his true parentage, though once he learned of it, desired nothing more than to assume his "rightful place" as heir to the Dreadfort. A violent, wild, unruly child from birth, his mother begged Lord Roose for aid in raising him. The Leech Lord sent her Reek, and the two would soon grow inseperable.
War of the Five Kings
Ramsay is feared throughout the North, and quickly gains infamy after the outbreak of the War of the Five Kings. He callously practices rape, murder, and other sick indulgences around the lands adjacent to the Dreadfort.
Ser Rodrik Cassel attempts to put an end to his atrocities after Ramsay forced himself upon Lady Hornwood. Rodrik's party comes across Ramsay shortly after he had raped and killed a peasant girl and his companion Reek had raped the corpse. Ramsay is able to survive by switching clothes with Reek, who is killed in his place. Ramsay-disguised-as-Reek is taken as a prisoner to Winterfell.
Ramsay manages to escape the dungeons of Winterfell while most of it's strength marches to defend Torrhen Square from Ironborn reavers. He flees back to the Dreadfort where he remains for the end of the war.
When Roose Bolton and his new wife Walda Frey learn they are having a child, Ramsay is incensed. Having already suspected Ramsay of murdering his first trueborn son, Domeric, Roose has no plans to lose another to his bastard. He arranges to have Ramsay killed.
The Bastard's Boys' Betrayal
When Robb Stark marches north to fight in the Battle for Castle Black, Roose and Ramsay accompany him. The Leech Lord instructs the Bastard's Boys - the band of murderers that Ramsay favours, but secretly report to Roose - to take Ramsay on a flanking maneuver against the Wildlings, but pull back, abandoning him. He then informs his son Ramsay that if he shows himself well in the coming fight, Roose would have him legitimized. With that, the stage was set.
When the battle was finally joined. Ramsay and his boys outstripped the main army, charging into the ranks of the wildlings alone. The Boys fight with Ramsay for a time, but fall back, as per Roose's orders. Ramsay fights hard, but he was never a skilled swordsman - he is slain, and his body is never recovered. Roose later disposed of the Bastard's Boys, to seal the knowledge of his deed forever.