I don't know if this is any use, but taken from
http://globalia.net/donlope/fz/songs/O_Mein_Papa.html
"O Mein Papa", once a hugely popular song (about the dead of a clown/father), was composed by Swiss composer Paul Burkhard (1911-1977) for the musical "Der Schwarze Hecht" (a.k.a. "Feuerwerk" in Germany), that premiered in April, 1939. The song reached #1 on the Sheet Music chart, and stayed in the chart for 26 weeks.
The song has been performed and recorded by Alan Breeze, Annette Klooger, Billy Cotton, Billy Vaughn, Connie Francis, Diana Decker, Eddie Calvert, Eddie Fisher, the Everly Brothers, Harry James, Ken Mackintosh, Lys Assia, Malcolm Vaughan, Muriel Smith, Ray Anthony & his Orchestra, Russ Morgan & his Orchestra, The Beverley Sisters, The Brasshats, The Radio Revellers, and many more.
The English lyrics were written by Geoffrey Clarmont Parsons and John Turner Phillips.
So I guess the original singer was whoever sang it in the musical. Eddie Calvert's version was a number one in the UK back in the 1950s, but was an instrumental version (Calvert being a trumpeter).