Leo Slezak (German pronunciation: [ˌleːo ˈslɛzak]; 18 August 1873 – 1 June 1946) was a world-famous Moravian tenor. He was associated in particular with Austrian opera as well as the title role in Verdi's Otello. He is the father of actor Walter Slezak and grandfather of the actress Erika Slezak.
Born in Šumperk (Mährisch-Schönberg), the son of a miller, Slezak worked briefly as a blacksmith, an engineer's fitter and served in the army before taking singing lessons with the first-class baritone and pedagogue Adolf Robinson. He made his debut in 1896 in Brno (Brünn) and proceeded to sing leading roles in Bohemia and Germany, appearing at Breslau and, in 1898-99, at Berlin. From 1901 onwards he was a permanent member of the Vienna State Opera's roster of artists, achieving star status.
Slezak's international career commenced in London at the Royal Opera House, Covent Garden, where he sang Siegfried (a punishing role that he would soon drop from his repertoire) and Lohengrin in 1900. (He would return to Covent Garden in 1909 after undertaking further vocal studies in Paris the previous year with a great tenor of a previous era, Jean de Reszke.)
Slezak secured a three-year contract with the New York Metropolitan Opera in 1909. Met audiences acclaimed him in performances of works by Wagner and Verdi. Along with Italy's Giovanni Zenatello, he became the most famous Otello of his generation, famously performing the role at the Met with Arturo Toscanini conducting.