It's John de Courcy, an ambitious Norman who thought it was easier to get forgiveness than permission, so on his own initiative he invaded Ireland with a small army and kicked ass, only to fall out of favor with the King. Norman Kings were big on personal initiative, but not without royal approval
The King sent a guy after him, a real teacher's pet named Hugh de Lacy, who managed to defeat John.
He was imprisoned and was only released when he promised to go on a pilgrimage.
He died obscure and poor in, errr, the 1220's or thereabouts iirc.