House Blackfyre is the cadet branch of House Targaryen founded by Daemon Waters, the eldest of the Great Bastards, when King Aegon IV legitimised his bastards on his deathbed in 184 AC and gave him the ancestral Valyrian sword Blackfyre. Daemon took the blade for his name and the arms of his royal father with the tinctures reversed, raising a black dragon on red against the red dragon on black of his half-brother King Daeron II.
Twelve years later Daemon I crowned himself on the steps of his keep and lit the First Blackfyre Rebellion. He and his eldest sons fell to the arrows of Brynden Rivers at the Redgrass Field, but his half-brother Aegor Rivers, called Bittersteel, carried his sons and the sword Blackfyre across the Narrow Sea and founded the Golden Company to keep the black dragon's cause alive in exile.
Four more rebellions followed across a century. Daemon II was taken at Whitewalls; Haegon I was cut down after his surrender; Daemon III fell to Ser Duncan the Tall at Wendwater Bridge. The line ended in 260 AC on the Stepstones, when Ser Barristan Selmy clove the heads of Maelys the Monstrous in the War of the Ninepenny Kings. With Maelys died the last male Blackfyre, though the Golden Company marched on under his banner for another generation.