Hi, I’m a dungeon master of about 4 years. I recently have been faced with a bit of an issue. I have a player in my group that I’ve had in my campaign over the last couple years. We are starting up a new campaign soon and I’ve provided the players with some options for potential factions and associations that exist in the world. One of my players (I’ll call him bob) didn’t seem interested in any of the options I provided. At first I just figured none of the options I made really called to him, so I suggested that he tell me what sort of faction he would need for his backstory. He gives me some really strange considerations like making a fair that holds riddling competitions, and some other very specific things. I was a bit confused by all this, but I attempted to put together something that loosely followed his suggestions. When I had finished connecting this faction into my worlds lore, I showed him what I had made for him. 

He had a lot of problems with it and began telling me that it was different than what he wanted. Confused at why he wanted such specific details changed, I began suspecting something was up. I did some searching and I’ve come to discover that the whole thing was beat for beat ripped from the dark tower series. I do some more searching and it turns out pretty much his entire backstory is composed of snippets from different Stephen king books. 

I don’t necessarily mind players using their favorite books or movies as inspiration for their characters, but this is a little more than mere inspiration. I’ve never dealt with anything quite like this before and I am concerned that he will continue to be disappointed by anything other than a nearly identical faction, plot, and backstory to that of Stephen king. On one hand, I know that he loves Stephen king books and I don’t want to tell him his character is not going to work in the story, but I’m also concerned that it could lead to more disappointment and problems in the future as I am not Stephen king and I am not tell that exact story. 

Has anyone dealt with anything like this before? Have you ever had a player that wanted to be (or closely mirror) a pre-existing character from some other media? Am I wrong and should just try to facilitate whatever character he wants to play? Any advice on how to handle this? Thanks

First up, just tell him that you know that his character is based on Stephen King books, and that those things don't exist in your world. Explain to him that regardless of what is in the backstory he creates, what exists in the game has to exist in the world that you've created. There has to be give and take when working out backstory. He is failing to understand that you, the DM, will create the threads of what happens next - he is imagining that the story will somehow play out in a way he has already determined.

You're giving too much leeway and allowing too much detail. You don't need factions either. Go back to the player and tell them to start over with the following:

• Pick a race and class
• Pick a Background
• Describe what their parents did for a living, whether they are still alive, any other family that they might have
• Describe why the character has a class and why they want to be an adventurer. Allow any instigating event in which the character plays a minor part
• Allow them to describe the type of any faction that they would like to be involved with. They describe the type: you, the DM, then tell them what's potentially available, where that faction exists in the world, and what it would be. Be flexible on this as much as you can, but ultimately there may not be rainbow-unicorn riding candy smugglers in your world. 
• Create one unexplained mystery from their past (could be magical in nature, could be a mystery NPC that visited them, whatever). Explain that over the course of the adventure, this mystery will be solved as part of a long campaign hook. Be clear that the player does not know the answer: only you know the answer. Examples from my current game: PC began as a baby washed up on shore with a burn mark on his face. Another killed a deer with glowing blue eyes, causing his goliath markings to vanish. Another's fencing master disappeared, leaving behind a book written in abyssal. Another entered the campaign at level 9, having been turned to stone 80 years ago (I needed to be able to introduce her mid-dungeon!).
• And that is it. That's all they get to determine from the beginning. There's no point in excessive backstory: they might be killed in the first combat encounter. Let the character grow as they develop.

The whole backstory should fit into half a side of A4, and absolutely no more.

I prohibit the use of anything directly taken from popular culture at my game table. In a campaign in which I was a player, one PC was literally a character from a book; in that book he commanded whole armies and destroyed nations. Now he was a level 1 Fighter. It made no sense whenever he mentioned his backstory and everyone just ignored it. There's a difference between inspiration and lifting it wholesale as you say.

So basically politely tell him it doesn't work and you don't want Stephen King stuff in your game.

This might work out just fine, so long as the expectation is understood by all parties that you are not someone else, and therefore, cannot be expected to mimic another person's work, style or story. You have your world, they agreed to play in it. That's the social contract that they need abide by. If they can't do that, I might suggest that you ask them to creat a new character, or suggest that they take their existing character to Stephen King and let him DM for them. (maybe not exactly like that, but you know your friends...do as you will.)

The world you have built can have whatever you want in it, factions, dragons, kindoms...whatever. But I would suggest that you get to choose what the world is made of, just as the players get to choose how their character is built. If there is something in a character background that absolutetly doesn't work in your world, just say so. There's nothing inherently wrong with telling one of you players "no" on this subject. You can, and have tried to make this a "no, but..." and this is as much as you really need to do here.

Again, just my 2cp.