House of the Dragon is a title that primarily references the Targaryen dynasty. The members of that noble family based everything on the mighty beasts that helped them claim dominion over the Seven Kingdoms. Their heraldry, iconography, nicknames, and aspects of their personalities seem to grow from the dragons. The series depicts quite a few winged monsters, but there's at least one legendary dragon that never appears in the series alive. Balerion, the Black Dread, is a historically important dragon, but what made him so special?