Mr. Mendel is a Swiss banker responsible for all monetary transactions during and after tournaments at Casino Royale.
While James Bond is recovering after being tortured by Le Chiffre, Mendel asks Bond for a password to the briefcase of the allotted money he won. Bond gives Vesper's first name as the password. Afterward, he gives his resignation from MI6 to M, and ventures to Venice, Italy with Vesper. A few days later, M calls Bond telling him that the winnings were never deposited in the Treasury's account. Bond tells her that he will call back, and proceeds to call Mendel. Mendel tells him the winnings are being currently deposited from the Swiss account, in which Bond discovers that Vesper is in the process of doing so.