Tywin was the first born son of Lord Tytos Lannister. Since his early years, he was forced to watch his mighty house nearly brought to ruin through his father's actions. His father while a gentle and amiable man was also weak willed and eager to please, loans went unpaid and his bannermen did what they pleased mocking him in their cups or openly defying him. House Lannister's reputation was low because of Tywin's weak father. Tywin had to take ruthless steps to rectify the situation restoring the family honor and fortune from its near ruin. Tywin took upon himself the task of putting down his two most unruly houses, House Tarbeck and House Reyne, for their defiance. He did so with ruthless efficiency, destroying both houses entirely so that their lines were ended, leaving their ruined and shattered castles as a mute testimony to the fate that awaits those who scorn the power of Casterly Rock. Such was the brutality of Tywin's destruction of House Reyne that a song called "The Rains of Castamere" was written as a tribute to the event.
He is the archetype of the powerful father. Obsessed with control and absolutely ruthless to enemies, he will destroy anyone who stands in his or his children's way. Tywin became cold and hard after spending a lifetime watching his kind and generous Lord Father being constantly manipulated and walked over by his bannermen and mistresses. He only became utterly cold after the death of his beloved wife, who was giving birth to Tyrion. Tywin is an extremely harsh and unforgiving man, terribly efficient at his job, and can't stand it when people laugh at him. It is well known that Tywin has never been seen smiling except on his wedding day and at the birth of Cersei and Jaime.
Believed to be responsible for hiring an assassin to murder Bran Stark while he lay in a coma, Tywin's son Tyrion is arrested at the Inn at the Crossroads by Catelyn Tully, the wife of Eddard Stark, current Hand of the King. She takes him to her sister Lysa, at the Eyrie, for trial. Though Tywin does not care about Tyrion's welfare, he sees the arrest and kidnapping as a direct slight on House Lannister's honor which he will not tolerate. In response Tywin sends Ser Gregor Clegane and his men, disguised as brigands, to sack and pillage various villages and hamlets across the Riverlands, Catelyn's homeland. These raids mark one of the seminal points in what is to become the War of the Five Kings.