If you're stuck in Vietnam on the same boat as Capt. Willard and you're looking for some light reading material to distract you from the horrors of war, you can pick up a newspaper and read an article about Charles Manson.
We see, at one point, that there really is a newspaper article about Charles Manson lying around on the boat. Why? Well, Manson was a charismatic cult leader who seduced a large group of people (known as the "Manson Family"), convincing some of them to commit horrible murders, including Sharon Tate, the pregnant wife of the famous director Roman Polanski, and several of her friends.
Manson's a lot like Kurtz—a charismatic cult leader whose followers worship him like a god. They're both part of what the novelist Philip Roth has called "the indigenous American berserk" (source).