From Bulbapedia, the community-driven Pokémon encyclopedia.
Team Galactic scientists are either members of or contracted by Team Galactic that help design and create new machinery for Team Galactic's plans like using the Lake trio to craft the Red Chain extracted from them and are dedicated to experiment on Pokémon like Team Rocket scientists.
In the games
Some of the scientists join Team Galactic to earn money and get power. Both they and the Galactic Grunts are located in the Galactic Eterna Building and the Team Galactic HQ to prevent the player from taking their plans down.
This is the only Pokémon they battle with: