From Bulbapedia, the community-driven Pokémon encyclopedia.
The Hall of Fame is a record kept by the Pokémon League of all the Pokémon trainers who have ever beaten the Elite Four and the Pokémon Champion. As seen in the games, the Trainer's ID number, name, and Pokémon team are recorded. For each Pokémon of the player's party, the species, name, gender, level, and area met are recorded.
In pokemon Red or Blue if the player encounters missingno the hall of fame data may get corrupted by a glitch in the game. however missingno was removed in Pokémon yellow except for the mew glitch.