Blackfyre is the ancestral Valyrian-steel sword of House Targaryen, borne by Aegon the Conqueror through the wars of the Conquest and passed from king to king for one hundred and eighty-four years. It is the larger of the two Valyrian blades the Targaryens carried out of the Doom, paired with Dark Sister, the slimmer woman's blade once wielded by Queen Visenya.
On his deathbed in 184 AC, King Aegon IV legitimised his bastards and gave Blackfyre to the eldest of them, Daemon Waters, who took the sword for his name and rose against his trueborn half-brother. Twelve years later Daemon I crowned himself, and the First Blackfyre Rebellion ended on the Redgrass Field beneath the arrows of Brynden Rivers. The sword was carried from the field by Aegor Rivers (Bittersteel), who took it across the Narrow Sea with Daemon's surviving sons and the Golden Company.
The blade has not been seen in Westeros since.