I’m starting a new campaign (I’m a new-ish DM) with some of my friends and one of the players refuses to make an original character. I’ve told the group multiple times to not base their characters on other characters from fiction. However, this player has done that once and had to remake their character because of it. Now, they are making a new character that is just based off another fictional character. I don’t want to seem like a stick in the mud, but it’s really getting on my nerves. The point of d&d is to make at least somewhat original characters; how can I convince this player of that?

tl;dr : a player in the campaign i’m running continues making their character completely based off of different fictional characters. How can i steer them away from that?