This interesting surname is an Anglicized form of the Old gaelic Mac Somhairle. The Gaelic prefix "Mac" means "son of", plus the personal byname Somhairle, itself a Gaelicized form of the Old Norse "Sumarlithr", composed of the elements "sumar", Summer, plus "lithr", warrior or mariner. It is interesting to note that an ancient Pictish document of North East Scotland refers to "the fleets of Somerleths" i.e. Vikings who made voyages to the British Isles in the Summer season-pirates, not settlers. Sumerleth was the name of a witness to the granting of a gift to the Abbey of Dunfermline circa 1169. The first recording of the Gaelic patronymic occurs in the early 13th Century, (see below). One, Alexander M'Sommarrli, noted in Glassrie, Ayshire, in 1355, is believed to have been a member of the Lamont clan who used the name M(a)c Sorley for several generations. The M(a)c Sorleys of Letterfinlay in Lochaber, later called a sept of Clan Cameron, descended from Somerleth armiger to John of Yla, Earl of Ross and Lord of the Isles. A branch of the Scottish clan Mac Donald bearing the name M(a)c Sorley was one of the earliest galloglass families to settle in Ulster. The name is now widespread in Counties Tyrone and Antrim. The first recorded spelling of the family name is shown to be that of Ranal Mac Somhairle, Lord of Argyle, which was dated 1211, Records of Scottish Invasions into County Derry, during the reign of King William the "Lion of Scotland", 1165 - 1214. 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.