Why were Native Americans males always depicted as being shirtless? Did they really walk around shirtless all the time?

Hello OP. I've been watching this question and waiting for a satisfying reply. Since one hasn't arrived, it seems like I'll have to venture in here. I'm a cultural historian of imperial history, focused on how empire was seen and portrayed, and I study indigenous resistance movements.

It seems to me that a big part of your question deals with why are Native Americans seen shirtless, in terms of popular culture (here are three examples: one from a page in Herge's 1932 issue of 'Tintin in America', one from the Disney 1953 film 'Peter Pan', and the final one from the poster for Kevin Costner's 1990 movie 'Dances with Wolves'. http://imgur.com/a/oumu2). These are just three easy ones to dissect, but there are countless examples, and I agree with you that a predominate image of young 'Indian' warriors, displays them shirtless.

It's important to stress that the indigenous group these artist are drawing from in order to create stereotypical images of 'Indians' are the people of the Great Plains. In the Tintin example, they even claim they are members of the Blackfoot confederacy. In the Costner example, the actors are suppose to be Lakota [edit: And in the Peter Pan example, we see the teepee and headdress icons, but the 'braves' are most likely shirtless so that they can show off the 'redskin' colour Disney artists employed- of which their insertion into the cartoon is purely so that they can sing 'what makes the red man red?']

The Great Plains people, and specifically the Lakota, are where a lot of Anglo-American 'indian' iconography comes from. They lived in teepees, they were skilled horse riders and hunters, they created and wore war bonnets most similar to the one that is most often culturally appropriated (just look at the cover of the Tintin I mentioned (http://imgur.com/a/SdukD) or another shot from Peter Pan (http://imgur.com/a/f3e5h). Interestingly the Lakota occasionally depicted themselves as shirtless (here is an example painted on a Lakota teepee: http://imgur.com/a/22sWb). People of the Great Plains were the united groups that made up the opposing forces in the Great Sioux/Black Hills war (1876-1877), which culminated in the infamous Battle of the Little Bighorn, where Custer was killed. Settlers constantly clashed with the indigenous groups they were displacing, but it is Little Bighorn that became the watershed moment in American history, and it is here were Native depictions are the most greatly exaggerated for popular consumption for decades after. For example, in 1881 John Mulvany painted a massive 11 by 20 foot 'heroic' last stand of Custer, which toured the country for 17 years and enjoyed massive popular viewings (http://imgur.com/a/TMWRm). If you look in the background (because of course the Indians should be background characters when trying to recast heroics to a spectacular defeat), you'll see shirtless warriors on horseback. Or look at the way Wild Bill's Wild West shows were billed when it came to London in 1887 (http://imgur.com/a/52YSP) contrasted to how the Native performers actually dressed during the shows, where they had some agency in how they chose to be portrayed (http://imgur.com/a/prOMl). Wild Bill's staged shows were in essence the foundations of the 'cowboy v. indian' TV trope, as well as where later depictions of the 'wild west' motifs are drawn. So today our images of the 'wild west' are basically copies of a copy of an original that most likely didn't exist in the way we think (see, for instance, Thomas J. DiLorenzo's 2010 article 'The Culture of Violence in the American West: Myth versus Reality').

Riding along side the propaganda of Little Bighorn are the popular images taken by Edward Sheriff Curtis. In 1906, robber baron J.P. Morgan commissioned Curtis to capture images of Native Americans just as the frontier was closing off. Curtis produced 1500 images (http://imgur.com/a/cigJw). These are most likely highly staged images. Taken alongside of Little Bighorn and the Wild Bill's media, we see an enshrinement of the shirtless, usually young, American indians or first nation warrior, often on horseback. A counterpoint to the 'cowboy' clad white frontiersmen.

One could also contrast this with the invented images of African subjected peoples, who were shown in little clothing in the literature, which was often the style of dress in equatorial climates, but more often used as a way to contrast between savagery and civilisation (think also about the images of African slaves, chained and in loincloths). In stripping down men, the image strips away a sense of status and the tailored made marks of 'civilisation'. It is a form of 'othering'. The image remains with us in a postcolonial sense as leaving the native american shirtless fits in with the new age notion of the Indian being directly connected to nature. Both viewpoints come out of a colonising gaze and are rooted in depicting a counterpoint to the industrialising, urbanising, christian America pushing west on their 'manifest destiny'.

For more on Edward Curtis, here is a second plug for a book by Timothy Egan, called 'Short Nights of the Shadow Catcher: The Epic Life and Immortal Photographs of Edward Curtis'. It's journalistic but easy reading.