That's Rorschach. He's not an Existentialist, he's a Nihilist... Of course, frankly, it also played into his egotistical Nihilism. He'd been looking for a long time for something to die for, I'd argue.
More than that. He's a hardcore Randian Objectivist; an extreme version of Steve Dikto's The Question and to an extant, Mr. A.
See:
http://en.wikipedia.org/wiki/Objectivism_(Ayn_Rand)
http://en.wikipedia.org/wiki/Question_(comics)
Alan Moore on the subject
CBA: Do you recall The Question?
Alan: Yes, I do. That was another very interesting character, and it was almost a pure Steve Ditko character, in that it was odd-looking. "The Question" didn't look like any other super-hero on the market, and it also seemed to be a kind of mainstream comics version of Steve Ditko's far more radical "Mr. A," from witzend.
(later...)
CBA: Did you explore her philosophy?
Alan: I had to look at The Fountainhead. I have to say I found Ayn Rand's philosophy laughable. It was a "white supremacist dreams of the master race," burnt in an early-20th century form. Her ideas didn't really appeal to me, but they seemed to be the kind of ideas that people would espouse, people who might secretly believe themselves to be part of the elite, and not part of the excluded majority. I would basically disagree with all of Ditko's ideas, but he has to be given credit for expressing these political ideas. I believe some feminists regard Dave Sim in much the same light; they might disagree with everything he says, but at least there is some sort of sexual-political debate going on there. So I've got respect for Ditko.
(later...)
CBA: Just to map this out: The prototype for Rorshach was The Question, right?
Alan: The Question was Rorschach, yep. Dr. Manhattan and Captain Atom were obviously equivalent. Nite-Owl and the new Blue Beetle—well, the Ted Kord Blue Beetle—were equivalent. Because there was a pre-existing, original Blue Beetle in the Charlton cosmology, I thought it might be nice to have an original Nite-Owl. I can't really say that Nightshade was a big inspiration. I never thought she was a particularly strong or interesting female character. The Silk Spectre was just a female character because I needed to have a heroine in there. Since we weren't doing the Charlton characters anymore, there was no reason why I should stick with Nightshade, I could take a different sort of super-heroine, something a bit like the Phantom Lady, the Black Canary, generally my favorite sort of costume heroines anyway. The Silk Spectre, in that she's the girl of the group, sort of was the equivalent of Nightshade, but really, there's not much connection beyond that. The Comedian was The Peacemaker, we had a greater degree of freedom, and we decided to make him slightly right-wing, patriotic, and we mixed in a little bit of Nick Fury into The Peacemaker make-up, and probably a bit of the standard Captain America patriotic hero-type. So, yeah, these characters started out like that, to fill gaps in the story that had been left by the Charlton heroes, but we didn't have to strictly stick to that Charlton formula. In some places, we stuck to it more closely, and in some places, we didn't.
see: http://www.twomorrows.com/comicbookartist/articles/09moore.html