Science: Richard Dawkins
Reason: Daniel Dennet
Progress: Sam Harris
Equality: Christopher Hitchens.
I'm pretty confident about the first two, and fairly sure about the second, but they're less obviously portrayed. In fact, Hitchens looks significantly better in the comic than in real life, or at least many years younger.
At any rate, go read it. Poke around too, the rest of the comics are quite funny, and worth the annoyance of navigating the site (which isn't exactly like most webcomics).