Sir Brian O'Rourke was first king and then lord of West Breifne in Ireland from 1566 until his execution in 1591. He reigned during the later stages of the Tudor conquest of Ireland and his rule was marked by English encroachments on his lands. Despite being knighted by the English in 1585, he would later be proclaimed a rebel and forced to flee his kingdom in 1590. He travelled to Scotland in early 1591 seeking assistance from King James VI, however, he was to become the first man extradited within Britain on allegations of crimes committed in Ireland and was sentenced to death in London in November 1591.

The Kingdom of West Breifne or Breifne O'Rourke was a historic kingdom of Ireland that existed from 1256 to 1605, located in the area that is now County Leitrim. It took its present boundaries in 1583 when West Breifne was shired and renamed Leitrim, after the village of Leitrim, which was an O'Rourke stronghold. The kingdom came into existence after a battle between the ruling O'Rourke clan and the ascendant O'Reillys caused the breakup of the older Kingdom of Breifne and led to the formation of East Breifne and West Breifne. The kingdom was ruled by the O'Rourke clan and lasted until the early 17th century, when their lands were confiscated by England.