Comedian Harmonists
The Comedian Harmonists were an internationally famous, all-male German close harmony ensemble that performed between 1928 and 1934 as one of the most successful musical groups in Europe before World War II. The group consisted of Harry Frommermann (tenor buffo), Asparuh "Ari" Leschnikoff (first tenor), Erich Collin (second tenor), Roman Cycowski (baritone), Robert Biberti (bass), and Erwin Bootz (pianist).
The hallmark of the Comedian Harmonists was its members' ability to blend their voices together so that the individual singers could appear and disappear back into the vocal texture. Its repertoire was wide, ranging from the folk and classical songs arranged by Frommermann to appealing and witty popular songs of the day by writers such as Peter Igelhoff, Werner Richard Heymann and Paul Abraham.
Read more at https://en.wikipedia.org/wiki/Comedian_Harmonists