This is an anglicized form of the Olde Gaelic name O'Cleirigh. The Gaelic prefix "o" indicates "male descendant of" meaning a clerk. An early 9th Century Cleireach (born 820 AD.) was of the lineage of King Guaire of Connacht, renowned for his hospitality. The surname is first recorded in the mid 10th Century, (see below). Other anglicizations of the name include (O) Clery, (O) Cleary, Clary and even Clarke. The O'Clerys originally belonged to Co. Galway, but by the 13th Century branches of the family had settled in counties Donegal and Derry where many members of the sept distinguished themselves as poets, churchmen and brehans (law givers). Two 17th Century scholars Micheal and Cucoigchriche O' Cleirigh helped compile "The Annals of the Four Masters", completed in 1636 and dealing with ancient Irish history. The first recorded spelling of the family name is shown to be that of O' Cleirigh of Co. Galway. which was dated c.950, The Annals of the Four Masters. during the reign of Power held by various Danish invaders at this time. 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.