Sir William Liath de Burgh (English: /dəˈbɜːr/ də-BUR; died 1324) was an Irish noble and Justiciar of Ireland (1308–09).
De Burgh spent much of his life fighting on behalf of his cousin, the 2nd Earl of Ulster, first coming to notice in 1290 when he was defeated in a skirmish with Mac Coughlan.
Returning from Scotland he was in Connacht by July 1316 and assembled "a motley army of Anglo-Norman colonists and Irish chieftains who had remained loyal to the earl and marched against Fedlimid O'Connor, who had taken advantage of the chaos to lay waste to the province.
[1] He had married Finola Ni Briain, daughter of Brian Ruad, King of Thomond,[2] by whom he had three sons: He may also have had other children- legitimate or illegitimate: Ronan Mackay summed him up as a loyal and capable lieutenant of the Earl.
The fact that Connacht did not collapse during the Bruce invasion was primarily due to William's ability and his strong ties to many of the leading Irish families of the province.