Domhnall O Lochlainn was King of Ailech. In 1083 he invaded Connaught, crossing into Ulidia, where he won the battle of Creeve in County Antrim in 1100. It is said that he cut down the great tree under which the kings were crowned. By 1091 he had become ruler of Ireland and in 1103 he defeated the Danes and Leinstermen at Donaghmore, County Down. He died in Derry.