 Clan Maclachlan claims descent from Lachlan Mor , who lived on the shores of Loch Fyne in the 13th century . Lachlan belonged to the family who originally emigrated from Ireland to Scotland in the 11th century . The progenitor of this family , Anrothan , son of <unk> O 'Neil , king of the north of Ireland , is said to have married the heiress of the King of Scots and gained lands campaigning there . Moncreiffe wrote that it was more likely Anrothan married a daughter of the local king of Argyll or a sub @-@ king of Cowal and through this marriage , Anrothan 's descendants gained control of the lands of Knapdale and Cowal , and several Scottish clans claim a descent from him including Clan MacNeil of Barra , Clan Lamont , Clan MacEwen of Otter , and the MacSweens who became the Irish Sweeney Clan who left Scotland and returned to Ireland in the 14th century as leaders of <unk> . 
