John de Courcy was a notable Anglo-Norman knight who played a significant role in the history of Ireland during the late 12th century. He is best known for his conquest of Ulster, where he established himself as a powerful lord. His military campaigns and strategic alliances helped expand his influence in the region. De Courcy was born around 1160 in England and became a prominent figure in the Norman invasion of Ireland. His legacy includes the founding of several castles, including Carrickfergus Castle, which served as a key stronghold in his territory. His life reflects the broader patterns of Norman expansion and settlement in medieval Ireland.