Pokémon Red Version, Blue Version, and Yellow Version - Trainer ID and OT Name
The trainer ID is 16 bits long. The player as well as each Pokémon can have a trainer ID. A Pokémon’s trainer ID is set to the player’s as the Pokémon is created, if it’s owned by that player. A player’s trainer ID is set when a new game is started.
Each Pokémon also comes with an Original Trainer name ("OT name"). This value, like the Trainer ID, is set to that of the player as a Pokémon owned by that player is created.
A Pokémon’s trainer ID and OT name must match those of the player in order to rename it with the Name Rater.
A Pokémon can disobey if, in addition to the player not having the appropriate badges, the Pokémon’s trainer ID is different from that of the player (see "Obedience check").
A Pokémon will gain extra Exp. Points (see the page " Experience ") if its trainer ID is different from that of the player.