Siegfried Müller is a retired German sidecarcross passenger and, together with his driver Reinhard Böhler, the first-ever World Champion in the sport.

[1] Siegfried Müller made his debut in the FIM Cup, a predecessor of the world championship, in 1974, in the last year of the competition.

They took out the title with an 88 point gap to the second placed team and also won the German championship.

[4] Müller raced Böhler in 1981 before retiring from international competition.

Müller's results in these three competitions were: Source:"SIEGFRIED MULLER GP RECORD".