Agatha is one of the Indigo League's original Elite Four Members in the Kanto based games (Red, Blue, Yellow, FireRed, LeafGreen, Let's Go Pikachu, and Let's Go Eevee), specializing in the Ghost type. She has a no-nonsense personality and a short temper, and also seems to have a long history with
Professor Samuel Oak, hating the idea of him creating the Pokédex.
Two years later, during the events of the Johto-based games (Gold, Silver, Crystal, HeartGold, and SoulSilver), it is shown that Agatha retired from the Elite Four, and is nowhere to be found.
Agatha resembles
Bertha quite a bit, enough so that
Shauntal writes about it in one of her books. She also may be a descendant of
Charm, but this has not been confirmed.
Pokémon the Series
Ash met Agatha in Viridian City. She was acting as the temporary Gym Leader for the Viridian Gym.