In Grand Theft Auto 4, players control Niko Bellic and explore the open world city of Liberty City. The game was released in 2008 for Xbox 360 and PS3. As an M-rated title, the target audience was ages 18 and up, though many 16-17 year olds also played it. As Niko, players can walk, run, drive vehicles, and use weapons to complete main missions and side activities. Popular features included the mobile phone, realistic pedestrian behaviors, 15 multiplayer modes, and a wanted system. Developing relationships with non-player characters provides benefits. The game sold over 7 million copies across consoles and allowed players to purchase real music heard in-game.