In the main series, each game's single-player mode requires the Trainer to raise a team of Pokemon to defeat many non-player character (NPC) Trainers and their Pokemon. Each game lays out a somewhat linear path through a specific region of the Pokemon world for the Trainer to journey through, completing events and battling opponents along the way. Each game features eight especially powerful Trainers, referred to as Gym Leaders, that the Trainer must each defeat in order to progress. As a reward, the Trainer receives a Gym Badge, and once all eight badges are collected, that Trainer is eligible to challenge the region's Pokemon League, where four immensely talented trainers (referred to collectively as the "Elite Four") challenge the Trainer to four Pokemon battles in succession. If the trainer can overcome this gauntlet, he or she must then challenge the Regional Champion, the master Trainer who had previously defeated the Elite Four. Any Trainer who wins this last battle becomes the new champion and gains the title of Pokemon Master.