Argilac Durrandon

Argilac Durrendon, also known as Argilac the Arrogant, is an unseen character in Game of Thrones. He is deceased when the series begins and has only appeared in "The Complete Guide to Westeros: House Baratheon" featurette. Argilac was the last of the Storm Kings, the rulers of the Stormlands since Durran Godsgrief, a legendary figure of the Age of Heroes and founder of Storm's End.

Background
When Aegon the Conqueror invaded Westeros, he sent his commander and rumored half-brother, Orys Baratheon, to take the ancestral stronghold of the Storm Kings. Argilac met Orys' forces in open battle and was soundly defeated. Afterward, Orys took not only Storm's End and the Stormlands, but also Argilac's black stag sigil, his words - "Ours is the Fury" - and his daughter, becoming the first Lord Paramount of the Stormlands and the founder of House Baratheon.

In the books
In The World of Ice and Fire it is revaled that Argilac was the leader of House Durrendon, the rulers of the Stormlands for centuries. After his death, Orys took the sigil and words of House Durrendon as those of House Baratheon.

Argilac got his nickname for arrogantly refusing Aegon's offer of marrying Orys (a bastard) to his daughter, cutting off the hands of Aegon's envoy and sending them back to him. He was also arrogant in engaging the Targaryens in open battle rather than withstanding a siege in the infamously impregnable castle of Storm's End. However, Argilac was motivated in this by having heard of the death of Harren Hoare in similar circumstances at Harrenhal, who prepared for a siege in his immense castle only for the Targaryen dragons to fly right over the walls. If Argilac resisted a siege by Orys it would only be a matter of time until the Targaryens directed their dragons to the castle, so wishing to avoid this fate Argilac met Orys in pitched battle.