Orys Baratheon

Rumored to be Aegon the Conqueror's bastard half-brother, Orys Baratheon slew the last Storm King in battle and took the man's castle, his daughter, and his sigil as his own. Houses have been founded on less. The crowned stag and the words Ours is the Fury both come down from that afternoon's work.

It makes the Baratheons the youngest of the great houses, and it gives the whole line its particular flavour: not ancient right but earned violence, a family that took what it holds and never pretended otherwise. Robert was very much Orys's descendant in that respect.