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