How do I get a new player to stop rewriting my game to match his favorite fiction?

I have a D&D 5e game that I’ve been running for a year that is on pause because some players don’t want to play online or go outside (stupid plague ruining my tabletop). So I offered my son and the player who still does small gatherings a filler game. My son picked Star Wars, I agreed. He told his adult sister, who wanted to come over with her boyfriend to join. During session zero I warned that Star Wars canon, for me, is the original trilogy and the original rulebooks from West End Games (1987).

In no time the boyfriend was saying his character is the cousin of Dash Rendar (who?) because that’s his favorite character. He defends his expectation because he bought himself a Dash Rendar miniature. Then, 4 sessions in, he wanted me to replace his ship, despite my effort to give him stats, background, drawings and floorplan, with Dash Rendar’s ship, because he bought a miniature for it (after having the other ship for a couple sessions). There is also the expectation that I make Dash a major NPC in my game, and give him Dash’s guns and equipment, and something about a planet; I stopped listening. I’ve never had a player like this (in 35 years). He’s not belligerent when I point the lines of ‘few’, ‘minor’ or ‘cosmetic’, or session zero. He just repeats the requests endlessly. And argues that they are still few, minor and cosmetic. And that’s just the character he wants to play. And he doesn’t see how making the game “enjoyable for him” should be such a hassle for me. It’s completely poisoning the game for me, I don’t even want to judge it anymore.

So to resolve it (dodge it entirely), I asked them if they would like to join my D&D game when social distancing stops or pauses or lightens or whatever. I thought it would help because they don’t have history with Forgotten Realms, so there wouldn’t be the crossed expectations. Since my son and his uncle are in both games, we could do some side adventures to level them up to toward the existing party, learn the rules and explain their characters’ relationships with the existing party. They said yes, and made D&D Beyond accounts to join my campaign. The boyfreind made a Warlock Hexblade. I was stoked to have eliminated the problem.

But now he doesn’t want to have anything to do with the Raven Queen, he wants me to replace her with some guy named Leoric from Diablo 2 because that’s his favorite console game. And I need to modify Shadowfell to be more like Diablo 2. And ALL of his spells and features and feats need a necromantic effect that mimic his favorite spells from the video game. I don’t want to hardline him, because I made concessions for every player, they just stopped demanding additional changes somewhere around ‘totally reasonable.’ And like my experience in the Star Wars game, a few concessions have already resulted in the expectation of more, more, MORE!

I pushed back, and he said that he wants to replace him with a Necromancer like Raistlin from DragonLance. Head:0, Brick Wall: Infinity

I am teetering on the edge of just telling him that I don’t try to play his PC, so he shouldn’t try to rewrite my game, and he’s welcome to go find another table where he can play Dash Leoric or whatever. Am I actually wrong, does this fall under the umbrella of ‘the judge’s first job is making the game fun for the players’ or is this guy hijacking my agency as creator and judge? If I am right, and discussing it does not work, what’s the next thing to try?

It does NOT help that it was my own dumb ass that invited my daughter’s boyfriend into my game in the first place. 🙂