In Season 4 of Supernatural, when Sam and Dean told Chuck that he was writing about events in their life that hadn't happened yet, he replied Obviously, I am God  with surprising conviction. Chuck went on to detail the kind of God he was.

Chuck is God (and also he has a sister). In the show's 14th season, it threw another twist Chuck's way: Not only is he God, but he's been the author of Sam and Dean's lives, and when Sam (Jared Padalecki) and Dean (Jensen Ackles) decided not to follow through on Chuck's story, well, they pissed him off.