So are Eric Burdon and Tony Sheridan, though I would hesitate to describe either of them as folk or blues acts.
However, if we are going to talk about real folk singers, let's talk about the magnificent Klaus der Geiger. He is a stunning fiddler, a live performer of enormous physical presence and he absolutely embodies the spirit of vital, immediate music, which is passed on face to face. Had he been born in an English speaking country, he would have been renowned throughout the world.
Hannes Wader is a fine interpreter of both German and translated songs. Liederjahn combine good taste and fine musicianship with a commitment, which easily crosses cultures. Their album of Yiddish songs still sounds fresh after nearly twenty years.
There is any number of groups playing medieval music - and doing it rather well. They don't get on TV, but you can hear them at the markets and pageants.
You can find brilliant blues guitarists anywhere and Germany is no exception. Werner Lammerheardt and Peter Finger are two of many.
Richard Bargel, Köln's slide guitarist, is able to get almost any musician he wants to play with him.
All in all, there is plenty of good folk and blues music to lap up in Germany.