Recorded as McLagan, McLaggan, McLagain, and possibly others, this is a Scottish surname which is also recorded in Northern Ireland. It is believed to derive from the ancient pre 10th century Mac giolla Adhagain, which translates as "The son of the servant of Adocan", which may be a form of Adam, and therefore probably would have had some religious significane. Many early Scottish and Irish surnames are associated with holy men, and in particulars those who were devotees of some significant biblical figure. They dont come much more significant than Adam. The surname is first recorded in the early 16th century when Donald Makclaagan appears as an assize witness trying to ascertain the ownership of the the lands of Grandtully, whilst the unfortunate John M'Gillenlarg was killed in a murderous attack in 1556, and thereafter for many years a reward was offered for his killer, although it does not seem to have been claimed. William McGalgane and John McIlglegane in two more exotic versions of the early spelling, were both arrested in 1613 for assisting members of the outlawed Clan MacGregor, whilst Duncan McClagan was presumably a more more peaceful sort, being the minister for Logierait in 1632.