Mac William Íochtar (Lower Mac William), also known as the Mayo Burkes, were a partly Gaelicised branch of the Hiberno-Norman House of Burke in Ireland. The territory covered much of the northern part of the province of Connacht. The Mac William Íochtar functioned as a regional king and received the White Rod. The title was a successor office to the Lord of Connacht which ended upon the assassination of William Donn de Burgh, 3rd Earl of Ulster, in June 1333.