Hunter J is a ruthless and cruel Pokémon bounty hunter around Sinnoh who catches and steals Pokemons and sells it in the Black Market for money. She appeared in Pokémon Diamond and Pearl, along with her army of henchmen whose primary means of transportation are advanced 6-wheeled armored proof trucks to take all captured Pokemon she caught to her airship and brings to the Black Market to sell. Her technology includes her huge airship with lasers and invisibility mpde, high-tech visor to sense Pokemon's teleportation (in case it got away using Teleport), and a system consisting of a gun to shoot out a gold cement to turn them into stone statues, and high-tech glass cases to temporarily hold Pokémon hostage for her clients. Hunter J never cares about the wellbeing of people or Pokemon and her own henchmen! Which marks her the most cold-blooded villian of all the series. J and her goons went down with their ship after it was hit by Uxie and Mesprit's Future Sight attack while capturing them for Team Galactic. She most likely met her demise in the huge explosion that followed presumably sending her, along with the rest of her crew, into the abyss of Lake Acuity. Team Rocket claimed to their boss Giovanni they were responsible for J and Team Galactic's defeat, causing their promotion.
Unlike other villains who have appeared in the series, she is one of the few ones who has not been defeated or being arrested by police when they're alert and on to her. J's Pokémon are Salamence, Ariados, and Drapion, which are so powerful that not even Ash and Gary together could defeat her. In an episode Ash and Gary were determined to rescue a group of Shieldon captured by her, Gary said to Ash that since they had recovered the Shieldon it was enough. Later on Ash teamed with a "High Ranked" Pokémon Ranger (in which he's called a Top Ranger) who's protecting a Riolu from J in order to bring it to her client and not even they could defeat her.
Hunter J has shown some interest in Ash's Pikachu, and it seems pretty rare in the Anime even when it used Thunderbolt and Volt Tackle. Also she likes Team Rocket's Meowth, most likely because he can speak Human Language. She managed to turn both Pikachu and Meowth into stone, but Ash and Friends along with Jessie and James managed to save all the Pokémon currently turned into stone.
Salamence is used for transport when she is on-field but also to brutally attack any interference with Hyper Beam and Flamethrower.
Drapion is in her Poké Ball. She seems to always rely on Drapion when battling Ash 1-on-1. Drapion could easily defeat Aipom and Turtwig at the same time. Arguably her most powerful pokémon, along with Salamence.