This is a... strange book.
The introduction (by another writer, written for 21st century audiences) recommends that you read it as a pastiche of the time it was written (mid-ish 20th century). The preface, by the original author, says that it should be read as essentially an American myth - the capturing in writing of the oral traditions of a nomadic people that become settled, in much the same way as happened for the European epics such as the Iliad, Beowulf, etc. Here, in place of Achilles, we have John Johnston, or Jeremiah Johnston, or Liver Eating Johnson/Johnston.
And here's why that doesn't quite work.
- The author, Raymond W Thorp, has a reputation for being elastic with the truth. Much of what transpires is clearly pulled from his own head.
- The primary source for virtually the entire book is White-Eye Anderson, a mountain man then in advanced old age interviewed by Thorp. Anderson is problematic because
a) By the author's own admission, he got most of his stories about Johnston from another mountain man, Del Gue, second-hand.
b) He was virtually at death's door when he was interviewed
c) He only knew Johnston briefly at the tail-end of his career, and was himself only a mountain man when the era was on the decline, and was likely eager to shoehorn himself into the tale of its glory days
d) Virtually all mountain men were famous embellishers, and were pretty loose with the truth, especially if it got in the way of a good frontier yarn to gullible tenderfeet.
What you end up with, then, is essentially a frontier literary version of barstool gossip of the "a friend of a friend told me" variety, but presented as historical fact. In it, JJ is a paragon capable of dispatching hundreds of foes in single combat, easily killing hardened warriors with his bare hands. Bearded and blond-maned, he supposedly towers 6'2'' and weighs 240-260lb. He also possesses a secret martial arts technique which he uses again and again to best his adversaries. That technique? kicking people really hard in the crotch (as far as I can work out from Thorp's sudden and uncharacteristic fastidiousness; he is quite prim about this one, despite describing scalpings and disembowellings in loving detail).
In summary, the book doesn't work as a work of history because if you GENUINELY believe John Johnston single-handedly dispatched hundreds of native americans, most of them in hand-to-hand combat, killed a bear with a bowie knife, was immune to pain, could snap bones with his hands and kill a man with one blow, and once fought off both a puma and a grizzly with the frozen, severed leg of a Blackfoot warrior, which he was using helpfully both as a snack and an improvised weapon (he had removed said leg from the man, incidentally, whilst he was still alive) well... then I have a bridge on the Thames to sell you.
It also doesn't work as a work of frontier mythology because Johnston as depicted in the book goes beyond being villainous and is just an out-and-out sociopath. While he is supposedly noble in his dealings with women (albeit the fact that he essentially purchased his wife from the Flathead Indians is glossed over) and kind to children, he callously slaughters and scalps scores of natives, including ones who were apparently minding their own business until Johnston turned up with blood in his eye. Although it's portrayed as either noble revenge or necessity, he butchers without compunction and even goes as far as leaving strychnine-laced biscuits for unwary Blackfeet to snack on, which is depicted as being the height of hilarity to him. He also hangs out with, and at one point leads, a gang of charming desperadoes who enjoy severing the limbs off their still-living native foes, among other things. And then there's the whole ritual disemboweling and liver-cannibalism, which even his contemporaries thought was a bit much. This man is meant to be a hero, mind you. We should judge people not by our values today but within the context of their time - were they good men by the standards of their age? Even with that lens applied, Johnston's actions were beyond the pale.
Problematic language and outdated attitudes in a book written decades ago don't bother me. Graphic depictions of violence don't bother me. The book is just not very well written. I didn't think I'd get bored of reading in loving detail about some poor soul getting scalped and then having his liver carved out, and yet here we are.