As The Hollywood Reporter pointed out, Hugh Glass was a real frontiersman, explorer, and fur trapper who traveled near the Upper Missouri River in the 19th century. That being said, early accounts of his life are unreliable and often fictitious. The Revenant is based on Michael Punke's 2002 novel of the same name, which was inspired by early 20th century poems that were lifted from the three earliest written accounts of Glass's adventures. Therefore, the depiction of those events should be taken with a pinch of salt as the authors of those texts didn't know Glass personally.
Some truths about the adventurer's life did make it into the story, though. According to History vs Hollywood, the cusp of the film's violent tale is based on a real botched adventure that played out close to the events in the movie. Glass was indeed attacked by a bear and left for dead by his fellow adventurers, including John Fitzgerald and Jim Bridger (played by Tom Hardy and Will Poynter, respectively). Glass gets payback in the movie, but he forgave his former comrades in real life. Of course, that's because the real Fitzgerald and Bridger weren't as rotten as they are in The Revenant.
