Austrian opera singer and film comedian, known for his performances of Wagnerian operatic roles.

Slezak made his debut at Brno (now in Czech Republic) in Lohengrin in 1896. By 1909 he had established his reputation in London and New York City as a heroic tenor in the part of Othello, and he won further esteem for his Wagnerian interpretations. In later years he abandoned singing and became known as a film comedian in Austria. His son, Walter Slezak (1902–83), a well-known American actor, wrote an autobiography, What Time Is the Next Swan? (1962); the title refers to his father's famous ad-lib in Richard Wagner's Lohengrin, when the swan moved offstage without him.