 Cassilis was known as the "King of Carrick" for the feudal influence he possessed in that region.Cassilis died in 1576 after falling from his horse.According to Robert Pitcairn, an early historian of Clan Kennedy, Earl Gilbert was a “werry greidy manne and cairitt nocht how he gatt land sa that he culd cum be the samin.” During the era of the Protestant Reformation, Earl Gilbert desired the Abbey of Glenluce and entered into transactions with the abbot in an effort to hold the abbey by feudal tenure.