Balerion, known as Balerion the Black Dread, was the dragon ridden by Aegon the Conqueror during the War of Conquest. He was so large it was said his shadow could swallow an entire town when Balerion took flight. Balerion was employed by Aegon the Conqueror to burn and half-ruin Harrenhal. Upon the climactic battle of the Field of Fire, Balerion, alongside the dragons of Aegon’s sisters, Vhagar and Meraxes, participated in the destruction of the largest army ever fielded against them.
During the uprising of the Faith Militant, Aegon and Visenya’s son, Maegor the Cruel, mounted Balerion and burned down the Sept of Remembrance with hundreds of members of the Faith Militant inside. Balerion is one of the dragons mentioned by Viserys Targaryen as he baths with Doreah in Vaes Dothrak.