Krakauer has a multi-faceted role in this book. First and foremost, he is a character, the narrator of the story he tells. Secondly, he is the author of this book. Third, he is a mountain climber.
At one time in his life, Krakauer was an avid climber. In recent years, however, he has given up the hobby. When Outside Magazine asks him to write an article about the commercialism on Everest, Krakauer knows immediately that he had to climb.
Of course, Krakauer gets more than he has bargained for. His expedition turns out to be the most deadly ever. He successfully summits Everest and also leaves the mountain alive, but takes with him not only the story, but questions.
Throughout the text, Krakauer attempts to figure out exactly what went wrong and what happened to whom. He does extensive research and painstakingly traces the actions of every climber on the mountain. He theorizes about the breakdowns of the expedition, and attributes the disaster to a series of small mistakes. He includes himself, and explicitly blames himself for at least one person's death. The experience affects him profoundly, and in addition to telling the story, the book focuses on how Krakauer is forever changed as a result of what happened.