Tin is a pokémon coordinator and trainer from Pokemon Iron and Amber and Pokemon Copal. If you choose the male character Iron than he appears as a member of the Elite 4 however if you choose the female character Amber than he appears as your contest rival, always showing up at your contests and challenging you.
It is implied that Tin comes from Fiore, he says that he comes from a desert place where there never used to be any Pokémon when you first challenge him at a contest. During your final contest when Team Rocket interrupts he shouts "Rocket? What about Team Snagem!"
Although it is never stated in the game it is confirmed that his twin sister is Cooper hence why they have such interchangeable positions.