From Bulbapedia, the community-driven Pokémon encyclopedia.
(Japanese: J) is a Pokémon Hunter (ポケモンハンター) that steals trainers' Pokémon for a profit. She first appeared DP020. Her Japanese voice actress is 本田貴子 Takako Honda.
She steals Ash's Pikachu and Team Rocket's Meowth, forcing Ash and the Rockets to work together to get them back. After a little confrontation with J, they managed to sneak into J's base and rescue their Pokémon. Though her minions have been captured by Officer Jenny, she has not yet been apprehended.
This listing is of J's Pokémon as of the most recent Japanese episode: