Seth MacFarlane is creator, writer, voice actor, Executive Producer for shows Family Guy, American Dad, etc.
In addition to the many religious gags on Family Guy and American Dad. . .
"I do not believe in God. I'm an atheist. I consider myself a critical thinker, and it fascinates me that in the 21st century most people still believe in, as George Carlin puts it, 'the invisible man living in the sky' " -
Seth MacFarlane to Steppin' Out magazine 
Seth MacFarlane “I’m an atheist, not to be a dick, but just cause it seems like the most likely scenario. But you’ve kind of got to envy the people who are living in this warm pillow…It’s a blessing, ironically, and a curse to be so pragmatic, because ya know, you do miss that cushion that a lot of people seem to have.”
Adam Carolla ..."I don’t approach 'is there a god' any different than I approach any facet of life which is : show me a little proof and I’m in, show me no proof I'm not in."
Seth MacFarlane “but we’re surrounded by people who don’t make that distinction. If you say to them ‘there’s a monster living in my closet, you can’t see him, but you gotta have faith that he’s there’ people would say ‘well that’s ridiculous, you’re out of you’re mind, you should be locked up’ but the same thing does not apply to a guy living on a cloud... We suspend our powers of logic."
Seth MacFarlane “religion notoriously claims that they invented morality, they didn’t. Morality exists in animals, ya know."
Seth on missing 9/11 flight Were significance junkies, we want to attach significance to everything.[We say] 'This must have happened for a reason.' And that's just not the case Coincidences do happen. They do happen."
As Stewie at Harvard
"Number three: Stay away from the church. In the battle over science vs. religion, science offers credible evidence for all the serious claims it makes. The church says, 'Oh, it’s right here in this book, see? The one written by people who thought the sun was magic?' I for one would like to see some proof that there is a God. And if you say 'a baby’s smile' I’m going to kick you right in the stomach." 
"They’re literally terrible human beings. I’ve read their newsletter, I’ve visited their website, and they’re just rotten to the core. For an organization that prides itself on Christian values—I mean, I’m an atheist, so what do I know?—they spend their entire day hating people. They can all suck my dick as far as I’m concerned."
Seth MacFarlane after being asked about Family Guy and American Dad repeatedly listed as the Worst Television Shows of the Week by the Parents Television Council. 
"There's no hell; you'll be fine."
Commentary on Family Guy: Blue Harvest around the Storm Trooper wedding gag
"Do I have that much contempt for Christianity? I guess maybe I do."
"The Big Bang has got a lot of support. Live with it."
Family Guy Season 4 Commentary
"I'm not a fatalist. I'm not a religious person. I'm sure there are close calls that we're not even aware of hundreds of times a year"
Talking about his experience with missing his flight on September 11th which was one that hit the North Tower of the World Trade Center.
"I'm still a man of science, not God." to Playboy, also about his experience on September 11th.
Crave Online: What does get cut by standards and practices?
Seth MacFarlane: Usually it is religion based. Usually if there is a joke that has to do with Jesus or somehow pokes fun at Christianity or Judaism or Islam or what not, usually that’s a problem for them.
Crave Online: Killing babies is fine?
Seth MacFarlane: I’m an atheist; so, I don’t give a shit.
Real Time with Bill Maher Interview, May 8, 2009 edition
Bill Maher: And, you are an atheist?
Seth MacFarlane: I am.
Interview with Esquire Published August 18, 2009
ESQ: Stupid hick? Speaking of which, I see you've recently become rather vocal about your atheism. Isn't it antithetical to make public proclamations about secularism?
SM: We have to. Because of all the mysticism and stuff that's gotten so popular.
ESQ: But when you wave banners, how does it differ from religion?
SM: It's like the civil-rights movement. There have to be people who are vocal about the advancement of knowledge over faith. 
Seth MacFarlane: I am.
Bill Maher: What do you think of the fact that it [atheism] seems to be a movement that is gaining credibility as of late.
Seth MacFarlane: I think it's about fucking time.
Bill Maher: People do seem to be coming out of the closet, in a way they didn't before my movie came out.
Seth MacFarlane: Hopefully that had something to do with it.
Bill Maher: I just think in general it's a movement. I mean the books, the movies, it's just about time.
Seth MacFarlane: People who have had eight years of basically being told nothing other than love Jesus and you'll be fine, y'know 9-11 and Jesus. And I think they are finally starting to come out of that and realize, wait a minute if he's wrong about this maybe this in fact is fundamentally wrong. I think there is still a long way to go. I think it's overly optimistic to think it's gaining popularity with any kind of speed, but
Bill Maher: Well it was on the front page of the New York Times this week, and a number of places around the country that you might not think it would be happening. When they put up a billboard saying atheists please call there wasn't any complaints just a bunch of people saying 'hey I want to join.'
Seth MacFarlane: In 200 years I think we'll be there. We have a ways to go.
Bill Maher: Yeah I agree, it's not gonna happen tomorrow.
Check out these most popular pages on Celeb Atheists (in order of popularity)
Morgan Freeman | Pat Tillman | Bill Gates | Hugh Hefner | Asia Carrera | Lance Armstrong | Seth MacFarlane | Angelina Jolie | Bruce Lee | Jack Nicholson | Bill Maher | James Cameron | Jodie Foster | Billy Joel | Matt Groening | Brad Pitt | George Clooney | Natalie Portman | Eddie Vedder | Isaac Asimov | Keanu Reeves | John Lennon | Noam Chomsky | Ricky Gervais