Aegon I Targaryen

"Aegon Targaryen changed the rules. That's why every child alive still knows his name, three hundred years after his death."

- Tywin Lannister to Arya Stark Aegon I Targaryen, known as Aegon the Conqueror, is an unseen character in Game of Thrones. He died almost three hundred years before the time of the series, and is not expected to appear. Aegon I Targaryen conquered much of Westeros with three great dragons, Balerion, Vhagar and Meraxes, and unified the realm under his rule founding the Targaryen dynasty. He was married to both of his sisters, Visenya and Rhaenys.

Background
Aegon I Targaryen was the first king of the Targaryen dynasty. He is the warlord who, with three great dragons and a small army, invaded and unified six of the Seven Kingdoms of Westeros in the War of Conquest. Afterwards, Aegon founded the city of King's Landing, built the Red Keep, and forged the Iron Throne from the swords of his defeated enemies, melted with dragonfire.

Season 1
Sansa Stark is given a history lesson by Septa Mordane whilst visiting the throne room in the Red Keep. Aegon the Conqueror is mentioned as the king who unified the Seven Kingdoms and forged the Iron Throne.

In Vaes Dothrak, Daenerys Targaryen and Ser Jorah Mormont discuss Aegon's invasion of Westeros and how he unified six of the Seven Kingdoms (the seventh, Dorne, was not added to the realm until some time later) some three hundred years ago. Jorah points out that Aegon had no "right" to the Seven Kingdoms, and never made any legal claim for his conquest: he conquered most of Westeros because he could. Daenerys points out that he could because he had dragons. Jorah expresses doubt that Aegon had dragons, indicating the events happened so long ago it's impossible to be sure.

Season 2
While at Harrenhal, Lord Tywin Lannister recounts to Arya Stark the history of the castle. King Harren the Black of the ironborn wanted to establish a legacy by constructing Harrenhal, the biggest castle ever built on the entire continent. Harrenhal was designed to defend against an attack from the land, and as Tywin muses, "a million men could have marched against its walls, and a million men would have been repelled." However, Harren did not anticipate an attack from the Targaryen dragons, who during the War of Conquest flew right over the high walls and attacked with dragonfire. As Tywin summed it up, "Aegon Targaryen changed the rules." Harren and all of his sons were roasted alive within their own hall by Aegon's dragons, and Harrenhal was left a blasted ruin. However, Arya Stark notes that Aegon was assisted by his sisters in his conquest of Westeros rather than acting alone.

In the books
In A Song of Ice and Fire, Aegon was a child of House Targaryen, dwelling on the island of Dragonstone in the Narrow Sea. The Targaryens, a family of Valyrian origin, had been in control of Dragonstone for a century before the Doom of Valyria destroyed their homeland in a volcanic cataclysm. For another hundred years on Dragonstone, the Targaryens slowly built up their strength and raised their dragons, the last in the world. When he was of age, Aegon, his two sister-wives and his three dragons led a scant few thousand troops in invading the entire continent of Westeros. Despite being vastly outnumbered, Aegon was able to secure victory after victory using his dragons. He smashed the Gardener and Lannister armies on the Field of Fire, securing their capitulation, and convinced the Arryns and Starks to join him peacefully through negotiation. Eventually all of Westeros acknowledged him as king, save only Dorne which he decided not to conquer after encountering fierce guerrilla resistance.

After the Conquest, Aegon ruled for thirty more years, apparently wisely and well. However, upon his death the realm was plunged into a bloody war when the Faith of the Seven rejected his sons, born of incest, from following him on the throne. Eventually the uprising was put down and the Targaryen rule secured for centuries.

In The World of Ice and Fire, it is revealed that Aegon was born 27 years before his coronation as king (and 25 years before leading the invasion of Westeros). He was the son of Lord Aerion Targaryen and Lady Velena Velaryon. Most if not all of the previous six generations of Targaryens born on Dragonstone were the product of incestuous marriages, but Aerion had no sisters - though by marrying a Velaryon he still ensured that his children were of pure Valyrian descent.

Aegon married both his sisters when all three were very young, but had already become dragon-riders. Aegon helped end the attempt by Volantis to conquer the other Free Cities, using his dragon to support the forces of Braavos, Tyrosh and the Westerosi Storm King in driving the Volantenes from Lys and Myr. In doing so, he confirmed that he had no interest in reforging a Valyrian empire in Essos.

Aegon began planning the invasion of Westeros long before launching the attack, spending time incognito visiting Westerosi cities and castles and gaining intelligence on the different houses, their lords and their vassals. He used this intelligence well in dividing the houses and winning the allegiance of some of the houses against the others. He was helped in the planning by his bastard half-brother, Orys Baratheon, his most loyal ally and vassal, his best friend and the first King's Hand. When Argilac the Arrogant offered Aegon an alliance against Harren the Black, offering his daughter's hand in marriage to cement the deal, Aegon declined and instead offered Orys's. Argilac took that as an insult and cut off the hands of Aegon's envoy. Aegon used this as a justification for his invasion of Westeros.

Aegon I fortified his initial landing point at the northern shore of the mouth of the Blackwater River, a strategically very defensible position protected to the east and south by water, and surrounded by open plains which would expose any attacking army long before it arrived. After the conquest, Aegon ruled for some time at the crude boomtown which sprang up there, known as Aegonfort. However, it remained a ramshackle pile of wood and earth, so after some time he moved his seat back to Dragonstone, until such time as a proper new capital city could be built in the former location of Aegonfort. He had Aegonfort razed, while planning and construction of King's Landing continued. By the time Aegon I died, however, only the foundations of the city and tunnels of the future Red Keep were finished (thus apparently Aegon continued to rule from Dragonstone for the rest of his life, though he always intended to move the royal seat back to the mainland some day).

Aegon was considered an enigma even by his contemporaries. He was a very solitary man, and his bastard half-brother Orys Baratheon was said to not simply be his best friend, but his only real friend. Aegon only rode his dragon for travel or war, never pleasure, and did not ride horses in tournaments. While Aegon did weigh in on major decisions, he left most of the matters of day-to-day governance to his sisters - as well as to his later "Hand of the King" Orys. Aegon was ruthless to his enemies, but was always generous to those who surrendered.