Visenya Targaryen

Visenya Targaryen is an unseen character. She lived and died centuries before the events of Game of Thrones, and is not expected to appear in the series. She was the sister and wife of Aegon the Conqueror and helped him in his invasion and conquest of Westeros three centuries before the events of the series.

Background
Visenya was the sister of Aegon and Rhaenys, and was born on Dragonstone, the Targaryen stronghold in the Narrow Sea. Following Valyrian custom, she and Rhaenys both married Aegon. All three rode dragons, with Visenya riding the dragon known as Vhagar. Visenya also wielded the Valyrian steel blade Dark Sister in battle.

All three dragons were present at the burning of Harrenhal during the War of Conquest, and were later deployed at the Field of Fire, where they destroyed the largest army ever fielded against their troops and broke the back of resistence to their rule in Westeros.

Season 1
Arya Stark, whilst posing as a common serving girl in Lannister-occupied Harrenhal, reveals to Tywin Lannister that Visenya was a hero of hers. She shows knowledge of Visenya's role in razing Harrenhal.

In the books
In the Song of Ice and Fire novels, Visenya is said to have been the fiercer, more temperamental and more passionate of Aegon's sisters. She was a noted warrior but also had diplomatic skills. After the razing of Harrenhal, she flew on her dragon to Crackclaw Point and won the support of the native inhabitants by promising that they would hold fealty only to the Iron Throne and no other lords.

She bore Aegon one son, Maegor Targaryen, who later became a king known as Maegor the Cruel.