He is most famous for his collaborations with the electronic music band Kraftwerk. He has created most of their sleeve designs since 1973. (On some later albums, the credits are obscure enough to cause some doubt as to the extent of his contributions.) He also co-wrote the lyrics of some famous Kraftwerk songs.
For a short while around 1973, Schult also played guitar in the group; this was to be short-lived, since Schult by his own admission is not quite good enough to be a professional musician, and since the group had started to develop its synth-based sound it no longer had any use for a guitarist.