It is believed that the Clan Forrester is of Celtic origin. The founder of the clan is believed to be a man called Marnin Forrester who held lands in Dunipace, Stirlingshire in about 1200.
Sir Adam Forrester is the first confirmed Forrester from contemporary evidence and is also regarded as the first confirmed founder of the Clan Forrester. He was an ambassador, merchant, Provost of Edinburgh, Keeper of the Great Seal of Scotland and Deputy Chamberlain of Scotland. In 1376 he acquired the estate of Corstorphine in Midlothian where Corstorphine Castle once stood.