Because kids basically always end up doing the opposite of what their fathers want (except for that one guy with the long hair), Siddhartha ended up sick to death of all the toys and desired a spiritual life. The problem was, he thought that all the popular religions were silly and so he set out to come up with his own. So he thought for awhile, came up with nothing, and then decided to just rip off the more existential aspects of existing religions and change his name to Buddha, because Siddharthism just doesn't sound very friendly.
Buddha decided that there were four truths governing the world, which are that (1) life sucks, (2) that it sucks because we want stuff, (3) that if we stop wanting stuff it'll stop sucking so hard, and finally that (4) Buddha's 8-step program will make the sucking stop now.
Buddha's 8-step program, which his marketing department wisely insisted he call the Noble Eightfold Path, basically boils down to being nice to each other (a philosophy later supported by that guy with the sandals), but he fleshed that out into eight points because his professor wanted an eight-page paper.
After coming up with all this, Buddha started to seriously put on weight, and eventually passed on at a relatively old age. Afterwards his followers journeyed around the countryside in yellow robes, not really accomplishing anything other than ticking off people they met, until one of them got lucky and converted a king of some sort about two hundred years later. Because kings were really popular in those days, everyone jumped on the bandwagon and converted, and then later some people jumped on a boat and went elsewhere, bringing yellow robes and statues of the morbidly-obese Buddha with them.
There was also some stuff in there about something called karma, which basically means somebody's counting how often you act like an asshole, and transcendence, which basically means that if you ever stop wanting things entirely life will stop sucking entirely but you'll also effectively cease to exist, but you won't mind 'cause your life, such as it is, will totally kick ass. But frankly I don't really understand all that, I'm really stuck way back on the part where the ascetic who condemned indulgence became extremely fat.
And now I think I'm done. I really have no arguments with Judaism (though like Stewie I'm really not a hat person), and making fun of Muslims is like making fun of fish; it's easy as hell, but the fact that they don't seem to care makes it a good deal less satisfying. Then again, fish don't kill you for disagreeing with them, so perhaps I should shut the hell up.