After encountering a Gym Leader, member of the Elite Four, or another main member of the cast, such as Bill, Mr. Fuji or Celio, their name will be listed in the Fame Checker.
Once that individual is listed in the Fame Checker, talking to various non-playable characters, along with checking certain magazines, photos and journals in various locations throughout Kanto and the Sevii Islands will reveal tidbits on the various personalities that are named in the Fame Checker. These are listed in the Fame Checker automatically, and can be checked in the Fame Checker at any time.
The Fame Checker is obtained during the main story of FireRed and LeafGreen. Defeat the Rival at the North end of Cerulean City and he'll give it to you.
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