Burgh, William de (a.1164–1206), magnate, brother of Hubert de Burgh, earl of Kent and justiciar of England, was one of the new wave of Anglo-Normans to come to Ireland with John (qv), lord of Ireland, in 1185. In some earlier biographies he is confused with William fitz Audelin (qv), the king's agent in Ireland. De Burgh was one of the most prominent men involved in the annexation of the kingdom of Limerick in the last quarter of the twelfth century. When John, lord of Ireland, decided to fortify the border of his lordship of Waterford (1185), he probably entrusted de Burgh with the construction of a castle at Tibberaghny, which was permanently granted to de Burgh in June 1200. De Burgh's holdings in Tipperary were centred along the Suir from Tibberaghny to Clonmel and in the west of the modern county around Kilfeakle. In Limerick, de Burgh was granted lands in the west of the county, but his main holdings were along the south bank of the Shannon from Limerick to Lough Derg. His main task was to guard against the O'Briens; indeed he is generally believed to have married the daughter of Domnall Mór Ua Briain (qv) sometime before 1193. He also had custody of the royal castle and lands around Limerick and acted as the king's deputy in Munster till 1203. When the honour of Limerick was recreated for William de Braose (qv) in 1201, de Burgh was the only person exempted from his lordship. He was given a speculative grant of the whole of the province of Connacht by John sometime around 1195, in response to raids by Cathal Mór Crobderg Ua Conchobair (qv) (O'Connor), king of Connacht, into Munster. From 1199 on, de Burgh actively intervened in the politics of Connacht, attempting to make good this grant. His efforts were not always supported by the other magnates, but eventually he gained support by making generous land grants to men such as Hugh de Lacy (qv).
For three years de Burgh supported the claims of Cathal Carrach Ua Conchobair (qv) against those of Cathal Crobderg Ua Conchobair for the kingship of Connacht. He came to terms with Cathal Crobderg in 1202 and joined with him, killing his rival, probably after deciding that Cathal Crobderg would be more amenable to his control. The alliance was successful, but rumours of de Burgh's death caused the men of Connacht to massacre his retainers, forcing him to retreat. The alliance with Crobderg collapsed, and in February 1203 de Burgh launched a massive raid into Connacht. However, his success in Connacht was enough to draw the attention of the king, who became worried at the potential power of his subject. It seems clear that King John wanted to limit de Burgh's conquests, especially along the Shannon, till the crown fully controlled the vital areas around Athlone and Galway. De Burgh's successes were enough to push Cathal Crobderg to make peace with John on terms favourable to both. In July 1203 he was granted a safe conduct to travel to the king to answer charges laid against him by the king's agent in Ireland, Meiler fitz Henry (qv), and he was deprived of the custody of Limerick castle. By October he had made pledges, given hostages, and travelled to the king. A commission was set up in March 1204 to inquire into the complaints against him. In September 1204 all his lands except those in Connacht were restored to him, and he returned to Ireland. It seems clear that de Burgh's rapid success in Connacht was the very thing that caused his downfall. The king wished to limit de Burgh's influence in Connacht after he realised the potential power he had rashly given de Burgh in originally granting Connacht to him. To regain any of his lands in Connacht would require a renegotiation on terms more favourable to the king; but before this could happen de Burgh died in the winter of 1205–6, and was buried in the priory of Athassell, which he had founded some years earlier. On his death, his lordship was taken into the king's hands to hold till his son, Richard, reached his majority. Ironically, de Burgh's sudden death caused more problems for the king than it solved: without the threat of de Burgh, the king found that Cathal Crobderg was much less willing to come to terms.