Biermann is not only a singer/songwriter, together with Eva-Maria Hagen he has made a wonderful folk album "Nicht Liebe ohne Liebe".

The adjective "German" can designate a country (that's the way this word has been understood in this thread), but it can also designate a language. The German language is majority language in 4 countries (5?) and minority language in (to name just a few) Belgium, Denmark, France, Italy, Poland, Czech Republic, Romania.

With this broader meaning I'd like to add the Swiss singer/songwriter Manni Matter and the French folk musician Roger Siffer and his group.

All my other favourites have been mentioned already

Wolfgang