Forbes was originally called Forbais. It was derived from the Gaelic Forba for field, and the Pict suffix ais. This clan originated in the Donside in Aberdeenshire, which was once in the Northern Pict Kingdom. A colourful legend tells of how the ancestor of the clan, Ochonochar, won possession of the land by killing a bear that had been terrorizing the district. These rights were confirmed in a Royal charter dated 1271.
That same year the estate was converted into a barony. Alexander de Forbes was a fierce opponent of Edward I of England, and was killed while laying siege to Urquhart Castle (1303). His son died at the Battle of Dupplin (1332).
The clan rose to national prominence in the 15th century, largely through the activities of Sir John Forbes and his four sons.