This ancient and distinguished surname is of Old Irish origin, and is an Anglicized form of the Old Gaelic "O'Sleibhin", descendant of "Sleibhin", a personal byname from "sliabh", mountain, and originally given to one of magnificent bearing, or splendid stature. Traditionally, Irish family names are taken from the heads of tribes, revered elders, or some illustrious warrior, and are usually prefixed by "O", male descendant of, or "Mac", denoting "son of". The great O'Sleibhin sept were a branch of the Cenel Eoghain in Ulster, that is, belonging to that group of people descended from Eoghan, son of Niall of the Nine Hostages, a 4th Century King of Ireland. The sept was famous in the early medieval period for its poets, and several Ulster poets of the name are mentioned in the Annals of the Four Masters, as well as one who was chief poet of Oriel (Counties Armagh and Monaghan) in 1168. In a 1603 Survey of County Fermanagh, Munter Slevine (the Slevin or Slavin family) are cited as hereditary possessors of church property in Kiltierney from generation to generation. The birth of one John Slavin was recorded in County Tyrone in 1723, and on October 23rd 1855, the christening of Mary Ann, daughter of William Slavin, took place in Gateshead, Durham. The first recorded spelling of the family name is shown to be that of Giolla Comhghaill O'Sleighin, chief bard of Ulster, which was dated 1002, in "Ancient Records of Ulster", during the reign of Brian Boru, High King of Ireland, 1002 - 1014. 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.