In Germany, Wild for Winnetou
By Michael Kimmelman
An explanation for the Germans' fascination with Winnetou and other (Plains) Indians:
You might say that May has become a Rorschach of German identity. German “natural sympathy” for American Indians is rooted in ancient times, Dr. Zeilinger explained. The Roman historian Tacitus described German tribes as uncorrupted, primitive, fierce and at one with nature, a people on the edge of a corrupt and voracious empire. May tapped into that primordial Germanness and also into what became, by the mid-19th century, a growing interest in America and the wider world.
Some readers may misinterpret this as a positive message, but really it's negative. Winnetou the good Indian is the exception, not the rule. By partnering with Old Shatterhand and eventually adopting Christianity, Winnetou proves that the white man's ways are best.
In Winnetou, the main villains are a tribe of "bad" Indians. So the story is about how a good white man triumphs over bad Indians with a good Indian's help. In other words, an early version of the Lone Ranger legend.
The Hitler connection
Like other Germans, Hitler loved the Winnetou books too. It sort of make sense that he'd associate Aryan Germans with "uncorrupted, primitive, fierce" Indians like Winnetou. And the rest of the Western world with "a corrupt and voracious empire" intruding on his pure German state. In his mind, Jews were undoubtedly the worst example of how civilization made people decadent and degenerate.
You have to twist things a bit to see how Hitler interpreted the books. Old Shatterhand and Winnetou both represent good Christian Aryans. The bad cowboys and Indians both represent decadent Jews and other Europeans. Old Shatterhand and Winnetou inevitably dealt defeat and death to the bad guys.
If Americans defeated the real Indians and Old Shatterhand defeated the fictional Indians, that gave Hitler a template. As a good Christian Aryan, he'd defeat the "bad Indians" (Jews and other Europeans) threatening his sanctified Germany. Hence Karl Mays' books helped Hitler envision conquest and genocide.
For more on the subject, see The Winnetou Films and Germans Think They Own Native Culture.