Fair, golden haired and tall, their women beautiful, their men handsome, the Lannisters claim descent through the female line from the legendary Lann the Clever, a trickster of the Age of Heroes. In the songs that celebrate his deeds, Lann, using no weapons, only his wits, winkled the Caterlys out of Casterly Rock, and stole gold from the sun to brighten his hair.
They are of the blood of the Andal adventurers who carved out a mighty kingdom in the Western hills and valleys of Westeros. Their ancestors were Kings, the last of whom, King Loren of the Rock, knelt to Aegon the Conqueror after his armies were decimated by the Targaryen dragons on the Fields of Fire.
The gold of Casterly Rock and the Golden Tooth has made them the wealthiest of the Great Houses. Their sigil is a golden lion upon a crimson field. The Lannister words are Hear Me Roar!
The present patriarch and Lord of Lannister, Tywin Lannister, was the Hand of the King to Aerys II Targaryen before he fled King's Landing during Robert Baratheon's Rebellion. Robert's agreement to take his daughter Cersei to wife won the Lannister's and the west over to the Baratheon's cause. Tywin rode down to King's Landing and proclaiming his loyalty to the Targaryens, convinced King Aerys that he was there to save the city and defend the King. Aerys ordered the city gates open. It was then that Ser Jaime Lannister, Tywin Lannister's son, a knight of the Kingsguard, sworn to protect the King with his life, slit the King's throat with gold gilded blade, earning him the name, Kingslayer. The Lannister armies laid waste to King's Landing, raping, burning and killing in what was one the worst episodes of the city's history, the Sack of King's Landing. Princess Elia of House Martell, wife to Prince Rhaegar, and their young children, Princess Rhaenys and Prince Aegon, were brutally slain by Lannister swords.
Because the Queen Cersei is a Lion of Casterly Rock, the Lannisters have become very powerful at the Royal Court, perhaps even surpassing the Baratheons.