The concept of the Pokémon universe, in both the video games and the general fictional world of Pokémon, stems from the hobby of insect collecting, a popular pastime which Pokémon executive director Satoshi Tajiri-Oniwa enjoyed as a child. Players of the games are designated as Pokémon Trainers, and the two general goals (in most Pokémon games) for such Trainers are: to complete the Pokédex by collecting all of the available Pokémon species found in the fictional region where that game takes place; and to train a team of powerful Pokémon from those they have caught to compete against teams owned by other Trainers, and eventually become the strongest Trainer, the Pokémon Master. These themes of collecting, training, and battling are present in almost every version of the Pokémon franchise, including the video games, the anime and manga series, and the Pokémon Trading Card Game.
In most incarnations of the fictional Pokémon universe, a Trainer that encounters a wild Pokémon is able to capture that Pokémon by throwing a specially designed, mass-producible spherical tool called a Poké Ball at it. If the Pokémon is unable to escape the confines of the Poké Ball, it is officially considered to be under the ownership of that Trainer. Afterwards, it will obey whatever its new master commands, unless the Trainer demonstrates such a lack of experience that the Pokémon would rather act on its own accord. Trainers can send out any of their Pokémon to wage non-lethal battles against other Pokémon; if the opposing Pokémon is wild, the Trainer can capture that Pokémon with a Poké Ball, increasing his or her collection of creatures. Pokémon already owned by other Trainers cannot be captured, except under special circumstances in certain games. If a Pokémon fully defeats an opponent in battle so that the opponent is knocked out (i.e., "faints"), the winning Pokémon gains experience and may level up. When leveling up, the Pokémon's statistics ("stats") of battling aptitude increase, such as Attack and Speed. From time to time the Pokémon may also learn new moves, which are techniques used in battle. In addition, many species of Pokémon possess the ability to undergo a form of metamorphosis and transform into a similar but stronger species of Pokémon, a process called evolution.
In the main series, each game's single-player mode requires the Trainer to raise a team of Pokémon to defeat many non-player character (NPC) Trainers and their Pokémon. Each game lays out a somewhat linear path through a specific region of the Pokémon 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 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 Pokémon League, where four immensely talented trainers (referred to collectively as the "Elite Four") challenge the Trainer to four Pokémon 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 Pokémon Master.