William Donn de Burgh, 3rd Earl of Ulster, the "Brown Earl," (1312-1333) was the grandson of Richard Og de Burgh, 2nd Earl of Ulster via his second son John.

He was murdered in 1333 and was survived by an only child, Elizabeth de Burgh, Duchess of Ulster who married Lionel of Antwerp, third son of Edward III of England.

Upon the death of William Donn ("donn" is Irish for brown (hair), hence his nickname) the various factions of the de Burghs, now called Burke, began a civil war for supremacy.

The factions were headed by Sir Ulick Burke, 1st Mac William Uachtar or Clanricarde (d.1343); Sir Edmond Albanach Bourke, 1st Mac William Iochtar (d.1375); and Sir Edmond de Burgh of Castleconnell (k.1338), ancestor of the Bourkes of Clanwilliam in Munster.