Team Rocket

Team Rocket is a group of criminals in the Pokemon franchise. They Appear in the Pokemon anime, as well as the games Pokemon Red/Green/Blue/Yellow.

In the Games
Team Rocket is a criminal organization bent on ruling the world, getting rich, etc. They steal and kill Pokemon for their devious plans, under the leadership of Giovanni.

In the Anime
Team Rocket has the same purpose in the anime. The most well known figures that constantly interfere with the protagonists (and provide a cheap source of comic relief) are Jesse and James, and the Pokemon Meowth that accompanies them.

Also in the anime, but not in the games, Team Rocket is responsible for the creation of Mewtwo, by altering the DNA from a fossil of the legendary Pokemon Mew.