Blackfyre is a Valyrian steel bastard sword that originally belonged to Aegon I Targaryen, which he carried during his conquest of the Seven Kingdoms. Afterwards it became the treasured ancestral blade of House Targaryen, carried by kings and princes.

A little over a hundred years before the War of the Five Kings, King Aegon IV the Unworthy gave Blackfyre to his bastard son Daemon Waters, a great warrior, instead of his lawful son Daeron. Many thought that this was a sign that his father favored him to rule. Afterwards, Daemon founded his own cadet branch of House Targaryen, House Blackfyre—taking its name from the sword—and he himself became known as Daemon I Blackfyre.

On his deathbed, Aegon IV legitimized all of his bastard children, among them Daemon Blackfyre. Daeron succeeded his father as King Daeron II Targaryen, but eventually, Daemon Blackfyre rose up in a civil war to try to replace him on the throne, known as the Blackfyre Rebellion. The sword was lost at the end of the war.