In the Champions Universe, there exists a middle-aged writer named John Williams. In college, he wrote a fantasy story about a hero named Aveliel, and built the world of Via around his heroic deeds. What Williams doesn't realize is that he has a super power, and only one. Everything he writes becomes truth. So, as he wrote the story, the world of Via came into being, gradually shaping itself to fit his concept of it.
The problem is, Williams (who writes under a pen name) isn't terribly talented. In fact, he's a bit of a hack.
Still, despite the terrible reviews, his story appealed to a lot of different readers, and he wrote several sequels. When these started hitting bestsellers lists, he wrote more and more, until Aveliel's story filled ten books. Then, he wrote a sequel series, about the children of Aveliel. The fifth book flopped, and the critics tore it to pieces. Crushed, Williams signed an agreement with his publishers that he'd have editorial control over anything written about Via, but that future stories would be ghostwritten.
Because he retains editorial control, this falls under the domain of his power. So the ghostwritten stories, too, have been integrated into the world of Via. But because they're ghostwritten, they have a tendency to fall into even worse cliches than the original novels, and they step on and contradict one another.
Williams' power is a self-preserving one, though. Williams doesn't realize he has the power, and never will. When he wrote a story in high school about a beautiful transfer student moving to town and falling in love with him, he promptly forgot he wrote the story. When it happened exactly as he wrote it, he had no idea he'd brought about these events. He later stumbled across the story, and figured he'd written it down as it happened.
Via, meanwhile, has become its own entity, separate from Williams' influence. Every once in a while, a Vian Seraph will find out the nature of the world and go babblingly insane, but they're rare, and the residents of Via have dealt with them fairly well.
The idea behind this as a roleplaying setting is that, the only characters Williams controls are those he writes about. The PCs are outside his influence, and therefore are free to exercise free will. And they'll need to, because Williams' life hasn't been going too well lately. His wife (the aforementioned transfer student) has left him, his son hates him, and he's been expecting his royalty checks to be higher than they are, so he's living outside his means. Then one night, he gets blind drunk. When he wakes up, there's a first chapter of a new book on his computer. He doesn't remember writing it, but it's brilliant. It has everything his stories have lacked before: action right off the bat, intrigue, and well-fleshed-out and interesting characters.
Williams will be observing the events of the game, which will be writing themselves as they play out. He will not be interfering with the events of the game, because he'll be too grateful to have this story writing itself to sit down and write anything, himself. Plus, he doesn't even realize his influence over the world.