This is an Anglicized form of the Olde Gaelic patronymic "Mac Donnchadha". The Gailic prefix "m(a)c" means "son of", plus the personal name Donnchadha, a compound of the elements "donn" meaning "brown", plus "cath", a battle. Two separate septs of the M(a)c Donaghs existed in Ireland. The first belonged to the Connacht counties of Sligo and Roscommon. These M(a)c Donaghs were a branch of the great MacDermots (8th Century Kings of Connacht). The chiefs of the family were Lords of Tireril in Co. Sligo. The second sept, whose chiefs held the castle of Kanturk and were known as Lords of Duhallow, were a branch of the MacCarthys. Andrew MacDonagh (born 1738) accompanied Wolfe Tone in the Bantry Bay expedition of 1796. Thomas MacDonagh (1878 - 1916) was a leader of the Easter Rising (1916) and a signatory of the Declaration of Independence. The first recorded spelling of the family name is shown to be that of MacDonnagh which was dated 1659, in "Petty's Census of Ireland", during the reign of Richard Cromwell, known as "The Lord Protector", 1658 - 1660. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.