Walter Slezak (Viena, Àustria, 3 de maig de 1902 - Flower Hill, Nova York, 21 d’abril de 1983) va ser un actor de cinema i teatre d'origen austríac actiu entre 1922 i 1976. Va aparèixer principalment en pel·lícules alemanyes abans d'emigrar als Estats Units el 1930 i actuar en nombroses produccions de Hollywood.

Walter Slezak (3 May 1902 – 21 April 1983) was a portly Austrian character actor who appeared in numerous Hollywood films. Slezak often portrayed villains or thugs, most notably the German U-boat captain in Alfred Hitchcock's 1944 Lifeboat, but occasionally he got to play lighter roles, as in 1962's The Wonderful World of the Brothers Grimm. He also played a cheerfully corrupt and philosophical private detective in the 1947 film noir Born to Kill and appeared as Squire Trelawney in the 1972 version of Treasure Island.