William de la Marck[1] (1446–1485) was an adventurer of German extraction.
On 21 May 1484, a treaty was signed at Tongeren, whereby the de la Marck family forfeited its claims to the bishopric and supported Liège's struggle against Maximilian I, Holy Roman Emperor for the reward of 30,000 livres.
Bouillon castle was mortgaged to William de la Marck until the time of repayment.
William's cousin Érard de La Marck became prince-bishop from 1506 until 1538.
He is described by Sir Walter Scott as "William, Count of la Marck", in Quentin Durward.