House Baratheon are the rulers of the Stormlands, one of the Seven Kingdoms of Westeros. The Baratheon's are a relatively young house, being formed during the Targaryen conquest of Westeros. Orys Baratheon, a general of Aegon I, slew the last of the Storm Kings, marrying his daughter which gave him his title and land, Storms End.
The Baratheon's commanded from Storm's End as Lords, until a young Robert Baratheon rose up against the Mad King, Aerys II. With Aerys II dead and the remaining Targaryen's fled, Robert took the Iron Throne, becoming King of Westeros.
The Baratheon House now command the Seven Kingdoms from Kings Landing, while Storms End is held by Robert's younger brother Renly.