Stan is PBed by Shia Labeouf, and his player is Jerry.

For a good wiki entry on Stan Marsh as he appears in the TV show South Park, see his wiki entry here:  http://en.wikipedia.org/wiki/Stan_Marsh

I'm bringing him in from several years ahead.  He's sixteen, and a junior in high school.  What follows is a brief summary of how things have gone in the years between now and then.

Stan and his friends continue to have wacky adventures.  The specifics of these will be worked out on an as necessary basis, but if you've seen the shown you know the kind of crap they get up to.  Just imagine that getting worse as they get older.  He's been on-again off-again with his longtime girlfriend Wendy, although recently their relationship has seemed to stabilize a bit.  Or at least, it has stabilized until the next hairbrained adventure.

Not all has been peaches and roses, of course.  As usually happens, the group has waxed and waned a bit, and Stan usually hung out with the goths during these times.  This is where his unfortunate smoking habit came from.  It seems odd that he would smoke with asthma, but he considers himself free of it.  Intellectually he knows it's still there, but it hasn't acted up or caused him any problems in over a year, so he doesn't think about it too much.  While he hoped this would keep his older sister Shelley from bullying him, she just found something else to torment him about.  His father's flirtations with alcoholism continued, and has put Stan off drinking somewhat.  He might still have a beer at a party, but he hates the idea of getting truly drunk and has never done it once, mostly because he sees how wrecked his father is when he's drunk and doesn't want to become that.

Stan is often the peacemaker between his group of friends, most especially between Kyle and Cartman.  He usually does pretty well at this job, though it can at times tax his patience.  He's also gotten pretty desensitized to the weird and illogical things that often happen in South Park.  He won't bat an eyelash at the things that go on in this universe.  As far as he's concerned, he's seen more or less everything and an alternate universe that occasionally hiccups is nothing compared to what he's seen and done.  He's recently started looking to the future, preparing for college and even beyond.  Right now he's thinking a criminal justice degree, and then on to either a career as a PI, or training for the FBI at Quantico.

Some of the details of this backstory may change, if other people take South Park characters and want to create a communal backstory.