Doe, a Dear, a Dearly Disturbed Individual
John Doe—if that's his real name—is the mastermind behind the series of killings based on the seven deadly sins. But, he has erased all traces of his identity. As Somerset observes, "He's John Doe by choice." To that end, he cuts off the tips of his fingers in order to not leave fingerprints, which must make writing in his over 2,000 composition books very, very painful.
Doe wants to teach the world a lesson through his "work," work which involves killing a bunch of people in the most grotesque ways possible to highlight their sins—gluttony, greed, sloth, etc. "I'm not special," he says. "I've never been exceptional. This is, though. What I'm doing. My work." He also thinks he's been chosen by God. The police captain probably puts it best when he sums up Doe like this:
"About the only thing we know about that guy right now is he's independently wealthy, well educated, and totally insane."
Insane? Oh, yeah. Short-sighted? No … not really. Doe succeeds in his project: he wants to get attention, to make people think about sin, and to prove that the world is a cesspool. In fact, even though he admires Mills so much, Doe has a lot in common with Somerset. Both of them are fed up with the world's apathy, as Doe illustrates in his big speech:
"Only in a world this s***ty could you even try to say there were innocent people and keep a straight face. But that's the point. We see a deadly sin on every street corner, in every home, and we tolerate it, we tolerate it because it's commonplace, because it's trivial, we tolerate it morning, noon, and night. But not anymore. I'm setting the example. And what I've done is going to be puzzled over and studied and followed forever."
We know his thoughts aren't crazy because they're mirrored by the uber-sane Somerset. It's his methods that make him totally crazy. Feeding a fat man until he bursts. Forcing a lawyer to cut himself up. This is some truly psychotic stuff, and it takes the veteran Somerset (who has seen it all) to take it in stride. He even tells Mills at one point, "If John Doe's head splits open and a UFO should fly out, I want you to have expected it." With this guy, anything is possible.
Mills thinks Doe is evil incarnate, but Somerset, despite his anything-is-possible attitude, reminds him that, "he's not the devil. He's just a man." And men are capable of some horrible things. Doe is willing to become a martyr for his cause, killing Mills' wife to manipulate Mills into killing him. But, even though Doe is dead, that doesn't mean the "good" guys triumphed. Evil totally wins this game.