Damon is thought to be the first son of Loren Lannister and Gwynesse Greyjoy, but was actually fathered by Tyrius Lannister after the Lord was rescued from drowning by the Greyjoy woman shortly before the start of the second Greyjoy Rebellion.
Upon his return to the Rock, Loren informed Damon that his sister Ashara Lannister had "killed" his mother with her birth. A subsequent affair with the much older wife of one of his father's vassals and a penchant for drink left Damon's reputation in tatters.
Loren bemoaned the fact that Damon didn't seem to take training seriously and was once unseated by a young and plainly armored Jon Umber, "some jumped-up Northman, half as much direwolf as giant." The heir's many vices gave Loren plenty of opportunity for criticism throughout his life.
Damon was called back to Casterly Rock by Lord Loren Lannister after the Tournament at Harrenhal, where he was wed against his wishes to Aeslyn Targaryen, the Head of House Targaryen. He then led the sack of King’s Landing with the intent of placing Aerion Blackfyre on the throne, killing Joseph Baratheon during the attack and earning the nickname "Stagslayer."
Aerion Blackfyre, however, was killed by Varyo Velaryon minutes after taking the city, and it was revealed that the sack had been merely a pretense to place Damon himself on the throne. He was crowned King of Westeros, despite his reservations, and his father assumed the position of Hand of the King.
Together with Commander Robert Manderly and the Golden Company, King Damon joined Lord Orys Connington in putting down the subsequent rebellion in the Stormlands led by Ser Ulrich Dayne and his brother Martyn Dayne, Lord of Starfall. Months later, he rallied the Lannister's allies in the Seven Kingdoms and defeated the remaining Baratheon and Tyrell forces at the Battle of the Kingswood, slaying the former king Harys Baratheon in battle and ending the war of the Ascent of the Lion.
Damon traveled to Sunspear to negotiate a truce with Dorne and attend the wedding of Princess Sarella Martell. While returning through the deserts, his party was waylaid by Martell forces disguised as Baratheon loyalists in an attempted assassination. Ser Ulrich Dayne intervened, betraying his Princess paramour and saving the life of the King. He delivered Damon back to the capital, fulfilling a promise to Queen Aeslyn. After his return, Damon swore off drinking.
In King's Landing, Damon learned that his queen was tried for infidelity and had fled to Essos, where she died giving birth to twins. The Riverlands remained neutral and Marq Baelish agreed to release Randyll Frey in exchange for the crown's pardon for not fighting at the Kingswood. When Randyll was discovered to have died under mysterious circumstances, Damon ordered Aeron Greyjoy to burn the kingdom and then marched to force Lord Baelish to bend the knee. The lord fled instead, and Damon named Edwin Frey the Lord Paramount of the Riverlands, moving its seat to the Crossing. Damon returned to the capital and married his former wife's younger sisterDanae Targaryen in order to preserve his descendants' claim to the throne.
Damon's father died at the beginning of the third era from a heart attack during an argument about the return of Thaddius, who blamed his disappearance on his older brother in order to escape their father's ire and cover up the relationship he had with Jojen Stark. After a heated argument with Damon concerning the loss of her pregnancy, Danae fled the capital for Dragonstone. At the Tournament of the Hand, Lord Gylen Hightower accused the King of attempting to cover up her absence and severed his alliance with the throne, declaring himself King in the Reach.
Damon's aunt, Jeyne Lannister, along with Grand Maester Paxtor, sought to aid his sleeping issues with milk of the poppy disguised as a simple herbal tea. After noticing the drastic changes in the King's behavior and his impaired decision making, Rymar Royce brought an end to the treatment.
Damon marched to Oldtown after receiving a false letter supposedly from his sister Ashara Lannister, begging rescue. As the War of the False King culminated at the gates of the Reach's capital, Danae Targaryen arrived atop Persion and burned the enemy fleet in the harbor before slaying King Gylen Hightower and rescuring Ashara. When reunited, she demanded equal ruling powers and House Lannister Targaryen was formed.
Damon and Danae returned to King's Landing for a time before traveling to Casterly Rock and then Crakehall to attend the funeral of Lyle Crakehall. On the way, they stopped to meet with Terrence Fossoway and order the disbandment of the Faith Militant. The Queen gave birth to an heir, Desmond Lannister Targaryen, soon after returning to the capital.
After Thaddius Lannister's murder at Winterfell, Danae flew Persion North while Damon attended the Tournament of the Crossing. Upon returning to the capital, he announced his intent to cobble the major thruways of Westeros, beginning with the Kingsroad in the Riverlands.
A discovery of theft at a motherhouse named for Mellara Tyrell prompted Damon to investigate with Ser Benfred Tanner, a hedgeknight who became a sworn sword after killing Lord Ferment Redwyne (who was sought for the attempted assassination of the Westerosi monarchs). A mishap in their search for the culprit led them to take shelter in a brothel. Suspecting him of infidelity and angered over his lies concerning the death of the High Septon, Queen Danae ordered Damon to return to the Westerlands.
There he set to work repairing his reputation amongst the West's nobility, especially in light of recent actions taken to improve the lives of the smallfolk. Two major political scandals proved setbacks to this goal - first, the sentencing of a Lannett for the rape of a servant girl, and second, the defense of a peasant boy falsely accused of assaulting Jeyne Lannister's daughter, which resulted in a trial by combat where Ser Benfred Tanner killed Ser Gunthor Lannister.
He learned of his daughter's birth shortly thereafter.
In the sixth era, Damon learned of a ball Danae was hosting in the capital and decided to travel back to King's Landing with Ser Ryman Sunglass, Benfred Tanner, and his own squire, Abelar Greenfield, to attend it in disguise, hoping to convince her to forgive him. The trio was robbed on the road by men and women posing as mummers, but eventually made it to the Red Keep where Damon was successful in convincing the Queen to permit his return.
Soon afterwards, the three departed to investigate progress on and complaints regarding the roads project. After a Captain in Damon's army challenged a landed vassal to a duel for his daughter's hand, Abelar volunteered as champion to prevent Damon from having to do so. Damon knighted him, and the boy slew Ser Uthor Break-Back in the seventh tilt by accident after the knight refused to re-don his helm and charged prematurely. On the same journey, Damon visited Harrenhal to address complaints regarding its castellan, Tion Lannett, and decided to begin the search for a permanent lord to take his place.
After falling back into old drinking habits, Damon recieved an ultimatum from the Queen to either cease drinking or be banished to the Westerlands once more, for good. Damon did so, but Danae left to travel Westeros by dragonback and did not return for months, during which time Damon learned she visited her paramour Princess Sarella Martell.
Hurt by these actions and her general coldness to him, Damon went West again with their two children to rule from Casterly Rock, where he began a love affair with Joanna Plumm through letters. He also set to work cobbling the Gold Road and repairing relations with Westerlands lords.
Danae Targaryen, wife
Daena Lannister -Targaryen, daughter
Daenys Lannister-Targaryen, daughter
Tyrius Lannister, father (deceased)
Gwynesse Lannister, mother (deceased)
Loren Lannister, uncle/adopted father (deceased)
Thaddius Lannister, half brother (deceased)
Ashara Lannister, half sister
"He was selfish. He was arrogant. He was snide and sarcastic and prone to bouts of self pity and vanity in equal measures, but when Damon was happy - truly, genuinely happy - he had a smile that lit up the whole room." - thoughts of Ashara Lannister
"Drunk. Whoremonger. Irresponsible. Lazy. He'd heard them all a hundred times and maybe it was for that reason they no longer wounded him or garnered a reaction. As an arrogant young man at Casterly Rock, the titles made him laugh and he wore them with pride, reveling in what a disappointment he was to all those around him." - Blood and Whispers
"Damon could charm the gold out of your pouch and make you happy you did it. Though he'd have spent it all by the day's end." –Eddrick Lannett
"Patience is a trait that you lack, Damon. My brother lacked patience and he died at the end of an axe. Harys lacked patience and he died just the same. You would do well to learn from their lessons." - Loren Lannister
"The boy sometimes acts as if he were honorable... What honor he finds in the bottoms of his cups." – Loren Lannister
"The heir to Casterly Rock had spent his entire life clamoring for his father's approval, but Loren had only ever offered criticism." - Blood and Whispers
“Impatient boy... He was hard to teach - took him forever to learn the importance of listening and training itself.” – Tywin Marbrand
"I do what I can. Though Damon tends to be as wild and headstrong as his mother." The Hand's tight-lipped expression verged on the edge of a thin smile before cementing itself in a frown. "As I'm sure you've seen." - Loren Lannister
"Patronizing bastard... The boy had to learn some respect to earn it." - thoughts of Gylen Hightower
"Damon Lannister is the most conceited and arrogant l man I have ever had the pleasure to meet. Has he always been so smug, or did that only come after you and his father put a crown on his head?" - Sarella Martell to Varyo Velaryon
"Lord Loren used you as a puppet. You were your fathers tool, a pretty face to rule while he pulled the strings in the shadows, but now he's gone. You have the chance to start a new dynasty of power, to reshape the world, but if you collapse at the first sign of opposition then you'll never be remembered as anything." - Rymar Royce
"Oh you should have seen Damon Lannister in King’s Landing. I myself went for the Hand’s tournament, but the lion king was the true entertainment there. He would be able to learn a great deal from your fool about keeping many plates spinning at once.” - Godric Grimm
"Damon's chirpy yet macabre ramblings disturbed the Master of Laws. Lord Crakehall almost wished that, for the sake of familiarity, he was speaking to the uptight, displeased Lannister he had come to know." - thoughts of Eon Crakehall
“A drunkard. A whoremonger. Lazy. Irresponsible. Arrogant. I know what they call him. I called him the same names the first time I met him. I know his reputation. But that is not who he is.” - Danae Targaryen
"For all his faults, he was a clever man, and Orys could respect that." - thoughts of Orys Connington
“Four Lannisters have sat that throne in the last thirty years. Each of them believed in something different. My brother Tyrius believed in honor, above all else. My brother Loren believed in vengeance, at any price. [Damon] seems to believe in mercy.” - Jeyne Lannister
"You’re a clever man, and I hear you’re brave and quick in battle. Don’t be so fast to assume your success is solely luck.” - Danae Targaryen
“You seemed exactly like every king from the stories. You’re not.” - Benfred Tanner
“I am not a wise man, Ryman,” said Damon. “You try very hard to not be,” the Lord Commander replied softly. “It makes me wonder what exactly it is you want sometimes.” - Ryman Sunglass
"The man was not what he had expected in a monarch, nor was he what Baldric had heard in rumors. Damon Lannister was neither brawny nor frail, neither a titan nor a bookish waif. There was something in those eyes that Baldric hadn’t seen in years... He couldn’t pin down the perfect word, but intelligence seemed as close as he could get. Insufficient, but close." - Baldric Dondarrion
"It is dangerous for a man like you to take a zealot into your confidence.” “Because I am King, you mean.” “Because you are gullible.” - Jeyne Lannister