Grand Theft Auto III is a free-roaming action-adventure video game and is also the first true 3D game in the Grand Theft Auto series.

In Grand Theft Auto III, the player character robs a bank with his girlfriend and another accomplice, only to have his girlfriend turn on him. She shoots him and leaves him for dead in the alley. Though he doesn't die, the player character is arrested and sent to jail for his crime. A lucky break in the form of an attack on the police vehicle he's riding in, sets him free. With the help of other criminals, the player character works his way up through the organized crime scene, and eventually has the chance to enact revenge on Catalina.Wikipedia: Grand Theft Auto III

Grand Theft Auto III was one of the first 3D games to offer an open-world environment. Combining action, shooting and driving all in the same game, the player has the choice to take on missions or simply play around in the game world.Wikipedia: Grand Theft Auto III

Besides being one of the first open-world games, Grand Theft Auto III was also a game that pushed the limits of violence and mature content in games. In fact the Grand Theft Auto series has become synonymous with the ongoing debate about violence in video games, and is often the first game mentioned in political circles surrounding the debate. Grand Theft Auto III, while not the first game in the series, was the first game to become a commercial success and, in some ways, helped to resurrect the violent games debate that had been quiet since the early 90s.Wikipedia: Grand Theft Auto III