Supernatural is one of my favourite tv shows (rampant misogyny aside), and I am a firm believer that the character Chuck is, in fact, God.
Now, there are all kinds of things you can point to as evidence that Chuck is God, and you can read about them on the wiki, so I won't go into them here.
I'm here to talk about how brilliantly the show's writers handle Chuck as God, through his dialogue and actions. How understanding that he is God adds a new level to the character.
Something that's important to realise is that God, while able to take small actions (relative to his true power), is unable to do anything that goes beyond mere mortal capabilities, aside from maintaining the illusion that he is a prophet. Not out of literal incapability, but because of the consequences of a being of his power directly intervening. In Episode 6.11, Appointment in Samarra, Death gives Dean an object lesson in how one reckless act by a more powerful being, even done with good intentions, can lead to disastrous consequences. Remember that God in this universe is not infallible. His first beasts, the Leviathans, were flawed mistakes, and he created Purgatory to get rid of them. So after all this time, God has taken to other methods of helping, and only becoming directly involved when there is no other option.
Chuck's involvement with the Winchesters:
- In 4.18, The Monster At The End of This Book, when discussing Sam drinking demon blood, Chuck tells him he left that out of the books, because he was worried it would make him unsympathetic. "You gotta know that's wrong." God is all about free will, but that doesn't mean He can't offer some advice. He knows where the demon blood will take Sam, that it's key to freeing Lucifer and bringing about the Apocalypse. He's trying to help Sam make the right choice.
- In the same episode, Dean surprises Chuck, coming up with a plan he seemingly hadn't thought of by bringing Chuck to Lilith so the archangel protecting him will drive her off. This is where Chuck starts to see that the Winchesters have what it takes to impose their own free will and find solutions that his angels can't. This is important, because he probably expects Zachariah and the other angels to go ahead and let Lucifer be freed so that the apocalypse can play out. Here Dean shows that he might just be the one who can save humanity.
- In 5.01, Sympathy for the Devil, Sam and Dean are transported from the scene of Lucifer's escape, through time and space, onto a plane, moments before the cage opens. Yes, the Winchesters have failed to prevent Lucifer's escape, but God knows they still have the best chance of stopping the Apocalypse. It's a major Hail Mary play, to break the rules like this, but for being so rooted in the need for faith, it's in the Winchesters who God has found something he can believe in. When Sam and Dean arrive at Chuck's house, we learn that Castiel was apparently killed, but despite this, the archangel is gone. Chuck could have done a lot in the time he was off-screen.
- In 5.22, Swan Song, we see our ultimate evidence that Chuck is, in fact, God, when at the end of the episode, he comments on the difficulty of writing endings, and how nothing ever really ends. He seems happy with his work, having spent the episode reflecting on the series of tiny, insignificant, human events which led to Dean being able to convince Sam to fight against Lucifer's control, and hurl himself into the cage. It's almost perfect, as the pieces fall into place, and we see that the events of the brother's lives had to happen as they did, to make them strong enough to save the world, not with knives and guns, but with love.
Chuck's involvement with other people:
- In episode 5.09, The Real Ghostbusters, while stalling to give Sam and Dean time to lay the ghosts to rest, Chuck mentions that the girl he lost his virginity to later told everyone it didn't count. On my second watch of the series, this was my first clue that the writers were playing around with "Chuck = God" in various ways. It's a wonderful way to describe the birth of Jesus to the virgin Mary.
Chuck's involvement with angels:
- Chuck doesn't like being around angels much, and he maintains his guise when among them. At the end of 4.18, he concedes to Zachariah's command that he continue to write.
- But it's with Castiel that Chuck's true nature comes out, and we see him not only break many of his own imposed rules, but also show a level of true emotion he doesn't show often.
- In Episode 4.22, Lucifer Rising, Dean and Castiel surprise Chuck again, when they arrive to get his help finding Sam and Lilith. An archangel arrives and Castiel stays to hold it off while Dean goes to help Sam. There's a wonderful shot of Castiel and Chuck, standing side by side, as light fills the window. And before the scene ends, Chuck reaches up, places his hand on Castiel's shoulder, and gives him an encouraging half-smile. This is a major break in character for Chuck, who has so far been cowardly and desperate to be kept out of events. He certainly can't help or even offer much in the way of morale support for Castiel, who may die fighting a more powerful angel. But that's not what this is. This is a father, seeing the one son who's finally getting the point of this "free will" thing, and being proud of him.
- In 5.01 again, despite Castiel having "exploded", according to Chuck, he appears at full strength, and later reveals he doesn't know how he survived his battle. The only possibility is that God brought him back.
- Episode 5.22 has been mentioned above, as the ultimate proof of Chuck's divinity. But it's also the ultimate proof of his love for Castiel. Humans are expected to fight and make their own decisions. But angels were literally built to serve. The ones who've shown anything close to free will have all been selfish and destructive. Except Castiel. He's the one who took a stand, facing down Lucifer to give Sam and Dean a fighting chance. And he is killed for it. But, it gives Dean the space he needs to talk and reach Sam. And so, Castiel is put back together, restored, more powerful than ever. When all of your other children have been so blindly self-righteous, either slaves to doctrine or violent rebels, what father wouldn't break all the rules, again, and reward the one son who not only understood the lesson of free will, but used that freedom not to earn glory or become to hero, but to sacrifice himself so that someone else could save the day?
- Of course, Castiel still has a lot to learn, and makes plenty of mistakes from here on out, but by the end of Season 9, he understands that the angels need to learn free will, and to make their own decisions. If he succeeds, he will achieve something God obviously failed to do, surpassing his father.