Heinz Sieder (28 June 1920 – 20 August 1944) was a German U-boat commander in World War II and recipient of the Knight's Cross of the Iron Cross (). The Knight's Cross of the Iron Cross was awarded to recognise extreme battlefield bravery or successful military leadership. U-984 was sunk with all hands lost on 20 August 1944 in the Bay of Biscay west of Brest by depth charges from the Canadian destroyers HMCS Ottawa, and .