Last head: Unknown, taken over by Lann the Clever during the Age of Heroes (most likely 10,000 years ago).House Casterly was the ruling Major House of the Westerlands (which in those times was a kingdom of its own), before Lann The Clever took it over. Notable members: Durran 'Godsgrief', Argillac 'The Arrogant'įun fact, the Baratheons even stole House Durrandon's words: Ours is the Fury House Casterly.Founded: Age of Heroes, by Durran 'Godsgrief'.This was right after Aegon's Conquest in ~1AC. House Durrandon was the ruling Major House of the Stormlands (which again was its own kingdom in those days), until Orys Baratheon slew the last 'Storm King', Argillac 'The Arrogant', and took over. Some changes in the higher ones (at the Level of the Starks) do exist, albeit they were quite ancient.
However, these have mostly been among the Lower Houses. Yes there have been many instances of Houses moving up and down within the Feudal ranking system of Westeros.