Sir Donal Dubh O'Donnell[1] (Irish: Sir Domhnall Ó Domhnaill, died 14 September 1590) was a member of the O'Donnell dynasty of Tyrconnell in modern-day County Donegal. He was the eldest son of Sir Hugh McManus O'Donnell, the Lord of Tyrconnell for much of the reign of Elizabeth I.[2]