Anyone who has seen Bill Hader on Saturday Night Live or his supporting work in films like Superbad and Adventureland knows he's hilarious.  But did you know that Hader also writes for South Park?  I did not and now I do and I think we're all better for the experience.Steve recently interviewed Hader (who's doing press for Paul) and asked how he came to be credited as a creative consultant on season 12.  Hader explains how the writing behind the show works and that he's still on board as a consulting writer and will be going on a three-week retreat in April where showrunners Trey Parker and Matt Stone hash out their ideas.  For those curious as to how the South Park machine works, hit the jump.  The 15th season of South Park premieres Wednesday, April 27th at 10pm on Comedy Central.  You can expect Steve's full interview with Hader this week.How did you get credited as a creative consultant on the 12th season of South Park?BILL HADER:  I’m good friends with Trey and Matt.  They asked me to come in on their South Park retreat.  They have these retreats where you go to Seattle.  One year we went to Boston.  You just go and it’s like a dream.  You go to an awesome place and stay in an awesome hotel and just for a couple of hours a day you swim around in South Park ideas.  The first retreat I went on they seem to like…it just seemed to gel.  It’s mostly those guys.  I kind of hang out in the room.  That is where I met Vernon Chatman and we started writing stuff together and now we are writing that movie for Scott Rudin.  It’s very chill and then in the 13th season they actually brought me in as a writer and I actually wrote on the show for part of that season.  I’m doing it again this season too.   In April I’m going out there for three weeks.  It’s just awesome.  You hang out for a couple of hours just working out these ideas.  It’s very peaceful.  Just a couple of people in a room with Trey and Matt.  It’s like a dream come true.  But it really is those guys.  It’s like they are working out their idea and you are saying, “Oh, that is funny.” Or maybe it’s this or that, you know what I mean?  You kind of throw out ideas, they run with it, and make it insanely funny.