Michael Farr, author of "Tintin the Complete Companion", has suggested that Müller was based on Georg Bell who worked with the Nazis and was allegedly involved in an attempt to flood Soviet Russia with fake Roubles.
Cutts_The_Butcher:
Hitler could have employed him to flood the British economy with fake money
I have always found this argument a little weak since Puschov, the actual leader of the Black Island gang, has a very Jewish-like appearance.
In one scene, Tintin bursts into an office on the Black Island where he watches the Thompsons's aerial acrobatics on the TV. There he also finds a list of associates which includes the name Otto Steinkopf of Potsdam, which is in Germany.
If this was a German government plot, it would have quite likely have been handled by the Gestapo or Abwehr (German military intelligence) from Berlin.
For me the Black Island gang is just another bunch of crooks, but there have been instances of such characters being employed by the secret service. I'm thinking that Müller, having escaped from a British prison, would have made his way back to Germany. He probably had friends in high places and they would have found him a job in the Abwehr. Since Europe may have been a bit too hot for him (figuratively speaking) he would be sent to the Middle East to disrupt oil supplies.
Cutts_The_Butcher:
was trying to create a Fascist state under the name of Mull Pasha in Red Sea Sharks
Perhaps. Having adapted to the ways of the Middle East, he would probably also want revenge for the humiliations of "Land of Black Gold".