House Lannister of Casterly Rock is one of the Great Houses of Westeros, one of its richest and most powerful families and oldest dynasties.
Following Robert's Rebellion, House Baratheon of King's Landing was founded, which had been their puppet house during the War of the Five Kings.
The Lannisters rule over the Westerlands. Their seat is Casterly Rock, a massive rocky promontory overlooking the Sunset Sea which has had habitations and fortifications built into it over the millennia. They are the Lords Paramount of the Westerlands and Wardens of the West.
House Lannister's Heraldry consists of a golden lion on a crimson background, and their House words are "Hear me roar!", which are rarely mentioned. Their unofficial motto, which is as well known as the official one, is "A Lannister always pays his debts" - which is used much more often and mostly in negative context, though it can also be used in the original, literal sense.
The incestuous relationship of Cersei and Jaime had been concealed in a conspiracy. Their son Joffrey Baratheon had claimed the Iron Throne on the premise that he was actually fathered by the late King Robert Baratheon. Lord Tywin was a key supporter of his reign in the War of the Five Kings. The Lannisters continued to hold sway when Tommen Baratheon ascended the throne, with Kevan Lannister as Hand of the King and Protector of the Realm