Balerion

Balerion, the Black Dread

Born in Valyria, Balerion lived nearly 200 years, his shadow large enough to engulf towns. With teeth like swords and flames that melted stone, he was Aegon the Conqueror’s ultimate weapon.

From Fire & Blood:

Balerion’s last rider was Viserys I Targaryen (House of the Dragon), but even in his old age, he remained a symbol of Targaryen power. His skull alone was the size of a carriage.