Daemon Blackfyre is an unseen character in Game of Thrones. He is not expected to appear in the series, being long dead by the time it begins.
Daemon Blackfyre was the legitimized bastard son of King Aegon IV Targaryen and his cousin, Daena Targaryen. After his legitimization, he founded his own new noble House as a cadet branch of House Targaryen: House Blackfyre, named after the ancestral Valyrian steel sword of House Targaryen which his father gave him. He led a rebellion against his half-brother King Daeron II Targaryen, the legitimate Targaryen heir, but was defeated.
With Serena Blackfyre he fathered the twins Aegon and Aemon Blackfyre, and Daemon II Blackfyre.
Daemon, along with his bastard siblings is mentioned in the House Targaryen's entry of the book The Lineage and Histories of the Great Houses of the Seven Kingdoms. The tome mentions that he rose in rebellion against his half-brother but perished from wounds sustained at the Battle of Redgrass Field.
In the books
In the A Song of Ice and Fire novels, Daemon is mentioned several times. More of his backstory is revealed in The Tales of Dunk and Egg.
- Daemon Blackfyre at A Wiki of Ice and Fire (spoilers from the books)