He was born in Philadelphia, USA, on 03/19/1921. His real name was Leonard Keyser. He studied at the Academy of Vocal Arts in Philadelphia and completed his studies at the opera school of La Scala, Milan. He specialized in the leading tenor roles of the Italian and French repertoire. In 1959, he debuted at the Royal Opera House in London (Covent Garden), as Canio in Pagliacci. He sang the same role in 1961 at the Amsterdam Opera, which, combined with starting a family, was the springboard for his significant career in the Netherlands. He appeared in a number of operas, including the Metropolitan Opera in New York as Don José [Carmen] (1961), Philadelphia Grand Opera as Otello [Otello] (1962), Helsinki Opera as Samson [Samson et Dalila] (1962), Tel Aviv Opera House as Calàf [Turandot] and Don José [Carmen] (1962), the Theater Augsburg as Otello [Otello] (1968) and the Wiener Staatsoper as Canio and Otello. He also appeared in Austria, Belgium and Switzerland. During his career he has worked with major singers, such as Tito Gobbi and Maria Callas. Very early on he devoted himself to teaching and developed a method that bears his name and which is used for the treatment of stuttering and other voice problems. He sang in the recording of the opera Lucia di Lammermoor, opposite Maria Callas in the title role. He worked once with the GNO, singing the role of Manrico [Il trovatore] (1963/64). He died in Amsterdam on 17/05/1992.