The richest house in Westeros. They control the Westerlands, and their primary branch is seated at Casterly Rock. The Lannisters are powerful and controlling, and completely merciless to those they view as weak. They are effectively the royal house and become the nemesis of the Starks early on. Their words are "Hear me Roar", but they also have a second, unofficial motto—"A Lannister always pays his debts"—which is an invitation to good Samaritans and a warning to bad ones. Their members are beautiful, with green eyes and blonde hair, and their sigil is a golden lion.
The Lannisters are said to have descended from Lann the Clever, a legendary trickster who is sad to have sunlight for his hair and fooled House Casterly into giving him their seat Casterly Rock. They have reigned as Kings of the Rock for thousands of years until Aegon's Landing, when their last king Loren I was forced to bend the knee to the Targaryens after witnessing the sheer destruction they had wrought in the battlefield using their dragons. In return, the Lannisters were allowed to remain as Lords Paramount of the West.
They fell on hard times during the rule of Lord Tytos Lannister. He was a kind and gentle, but weak man that brought House Lannister to near ruin, as he loaned money to lords that never bothered to repay him and allowed his vassals to mock him at court or ignore his orders. Eventually his son Tywin brought the wayward bannermen to heel and restored the house to its former glory by quelling a rebellion among the two most unruly Houses, the Tarbecks and the Reynes. Tywin destroyed both Houses, killing every known member and setting up as a message for all that dare to cross him. Soon thereafter, Tywin was made Hand of the King by Aerys II, holding that position for many years. Over time, Aerys's madness grew, droving a wedge between the two, along with the king's lusting after Tywin's wife, cousin and trusted confidante Joanna. Tywin was never a jovial man, but when Joanna died birthing their third child, Tyrion, he was much saddened and his brother Kevan became his right hand. Their sister Genna took a maternal role over the children. His second brother Tygett died of a pox, and their brother Gerion sailed off on a journey to Valyria, never to be seen again.
During Robert's Rebellion, the Lannisters stayed neutral for the majority of the war. Only after the defeat of Prince Rhaegar at the Trident did Lord Tywin bestir himself to join Robert Baratheon against the Targaryen dynasty, perpetrating the Sack of King's Landing when the Lannister loyalist Grand Maester Pycelle suggested the gates be opened. There Ser Jaime Lannister, still a Kingsguard, slew Aerys, the last crowned Targaryen king. Meanwhile Tywin's knights killed the rest of the Targaryens in the capitol to prove their commitment to Robert's cause. Afterwards, Tywin's daughter Cersei was wed to King Robert. This marriage and the increasing amount of gold Robert owes to Tywin have only increased Lannister power. Much of Lord Tywin's energy is directed inward, ensuring all of his relatives do their part to uphold the family name. Unbeknownst to most, Lord Tywin's children Queen Cersei and Ser Jaime have, for most of their lives, carried out an incestuous love affair. All three royal children, supposedly King Robert's, are actually Jaime's.
When King Robert visits his old friend Eddard to offer him the position of Hand of the King, the Lannisters are suspected to have killed the previous Hand, Jon Arryn, and attempting to kill the young Bran Stark. Only the latter is true, for Bran had witnessed Cersei and Jaime's affair while Arryn was murdered by his wife.
Lady Catelyn captures Tyrion Lannister at a crossroads inn to bring him to trial, prompting Lord Lannister to send raiders to Tully lands in an attempt to draw Lord Stark into the field, hoping to capture him for an exchange. Eddard, however, is waylaid on the streets of King's Landing by Ser Jaime and is injured in the melee, sending other men in his stead.
Tyrion escapes of his own volition, but the war continues along with intrigue in the capital, where Cersei has Eddard arrested. Tywin and Jaime win several victories over the riverlords, but the Tullys are soon joined by Eddard's son Robb and a host of northmen. Tywin repels one Stark army under Lord Roose Bolton in the Battle of the Green Fork, but this force turns out to have been a feint: with Tywin distracted, Robb captures Jaime in a surprise attack, and breaks his siege of Riverrun.
Meanwhile Cersei fears for her children if Stark informs Robert of her childrens' parentage. She has her cousin Lancel Lannister, Robert's squire, supply the king with strongwine during a boar hunt, resulting in Robert receiving a mortal wound. Soon her and Jaime's son Joffrey has become king, and orders the execution of Lord Stark, ruining any chance of peace. Jaime, despite his absence, is named Lord Commander of the Kingsguard. Tywin, having been named Hand, sends Tyrion to take up his duties while he campaigns in the Riverlands. Meanwhile Robert's brothers Stannis and Renly Baratheon have each contested Joffrey's right to the Iron Throne, while Robb Stark was declared King in the North by his bannermen. So begins the War of the Five Kings.