Unger was born in Leipzig (Germany), and as a student studied Theology and music. He made his singing debut aged 37, going on to make appearances at Cassel, Zurich, Bremen, Neustrelitz, Brunn, Elberfeld and Mannheim.
He was recommended to Richard Wagner for the role of Siegfried by Hans Richter, and, after close supervision from a singing tutor, he performed the part in Siegfried and Götterdämmerung with great success at Bayreuth in 1876 and at other venues in the premiere of the complete cycle of Der Ring des Nibelungen, conducted by Richter. In the same cycle, Unger also played Froh in Das Rheingold.
- 'The New Grove Guide to Wagner and His Operas' By Barry Millington Published by Oxford University Press US, (2006) pg 25 ISBN 0-19-531128-0
- 'The American History and Encyclopedia of Music: Musical Biographies' Part Two By W. L. Hubbard Published by Kessinger Publishing, (2005) pg 419 ISBN 1-4179-0713-4