He was the man who with Breyan Mandragoran, Lain Mandragoran's wife, plotted the overthrow of the Seven Towers so that they might supplant the lawful lords of the Borderlands. Instead they managed to so weaken Malkier that when Trollocs invaded, the land had not a prayer. Cowin was labeled a Darkfriend.
He was captured by Jain Farstrider and then challenged by King al'Akir Mandragoran and killed in a duel after his treachery was revealed. This the king did because Gemallan, also called Fairheart, was considered a hero of the realm.