Early life
Aegon was from the island of Dragonstone, the westernmost outpost of the Valyrian Freehold, which his family had settled over a century before the Doom of Valyria. According to Targaryen tradition, Aegon married within the family; however, instead of just one sister, he married both of them: his elder sister, Visenya, and his younger sister, Rhaenys. All three were dragonriders before they were wed.
In the aftermath of Volantis's expansion and attack on Tyrosh, Aegon, the Lord of Dragonsone, supported Pentos and Tyrosh. Atop his dragon, Balerion the Black Dread, Aegon burned a Volantene fleet before it could attack Lys. After the defeat of Volantis, Aegon returned to Dragonstone.
The Conquest
Aegon decided to go west to Westeros, and for years he planned his conquest of the Seven Kingdoms. He made a huge table map of Westeros painted without any borders to signify that it should be one realm alone instead of many. This map later became known as the Painted Table. His plan was ambitious but eventually successful.
When Aegon was ready, he and his two sister-wives, Rhaenys and Visenya, landed with his army on the east coast of Westeros at the mouth of the Blackwater Rush, where he constructed the wooden Aegonfort. With the aid of their three dragons (Vhagar, Meraxes, and Balerion the Black Dread) Aegon led the Targaryen army to victory after victory, conquering or subjugating six of the seven kingdoms of Westeros and reestablishing the riverlands as a separate region. He failed to conquer Dorne, however, and eventually was forced to respect their autonomy.
Aegon chose to date the beginning of his reign from the day the High Septon anointed him in Oldtown. Rather than ruling from Oldtown or Dragonstone, Aegon chose to make his seat King's Landing, the new settlement growing around the Aegonfort. He also took the swords of his defeated enemies, forging them into the Iron Throne. Aegon also created the office of the Hand of the King and Orys Baratheon was made the first Hand.
First Dornish War
Knowing that Dorne was the Targaryens' only defeat, Aegon launched another invasion hoping to complete the conquest in 4 AC. The First Dornish War resulted in the death of Rhaenys Targaryen when a lucky shot from a scorpion took her dragon Meraxes in the eye, and the dragon crashed from the sky dead taking her rider with her. Aegon's wroth after Rhaenys's death knew no bonds.
Aegon and Visenya placed bounties on the heads of Dornish lords and in turn the Dornish put bounties on the price of the Targaryens. Aegon and Visenya were assaulted on the streets of King's Landing and if not for Visenya and Dark Sister they would have been killed. This attack led to the forming of the elite royal bodyguard known as the Kingsguard in 10 AC. Visenya personally chose the men herself. The attempted conquest of Dorne was called to an end in 13 AC after Aegon, atop the Iron Throne, read a mysterious message delivered from the Prince of Dorne.
Later life
Aegon spent much of his reign consolidating his power by traveling throughout the Seven Kingdoms and building his capital at King's Landing. During his rule he tread carefully with the Faith of the Seven, so they would not oppose him. Aegon built a grand sept on Visenya's Hill and agreed to the construction of an even grander one known as the Sept of Remembrance on Rhaenys's Hill.
King's Landing initially lacked walls as Aegon felt no one would assault a city protected by dragons. Realizing that he and Visenya were not always in the city, however, he ordered massive walls to be made to surround the city, with construction of the city walls and its gates completed in 26 AC.
Aegon found the Aegonfort was not suitable for a king, and it was torn to the ground in 35 AC. Aegon moved his family and court back to Dragonstone, while he commanded the construction of what would later be called the Red Keep. It was rumored that Aegon placed Visenya in charge of the building of the Red Keep so that he would not have to suffer her presence on Dragonstone. The Iron Throne remained at the build site instead of Dragonstone, since it was too heavy to be moved.
While at Dragonstone's Painted Table in 37 AC, Aegon died from a stroke while telling a tale of his conquest to two of his grandsons. Upon his death and the ascension of his sons, Aenys I and then Maegor I, several rebellions broke through out the Seven Kingdoms that eventually evolved into the Faith Militant uprising. War, death and chaos gripped the Seven Kingdoms that did not end until the reign of Aegon's grandson, Jaehaerys I