People with at least one Pokémon creature can be considered a Pokémon Trainer. In this sense, people in related Pokémon occupations, such as Pokémon Coordinators or Pokémon Breeders, can also be considered to be Pokémon Trainers.
Some Trainers carry a Pokédex with them, which serves as identification as well as a tool for keeping track of the Pokémon a Trainer has seen or caught. The process of completing such a list is known as "filling" the Pokédex. A Trainer who has filled the Pokédex (with minor exceptions) is a Pokémon Master. In the animated series, the Pokédex is already loaded with much of the information that a Trainer needs in order to identify Pokémon, but in the video games, the data of a Pokédex starts empty and must be gradually filled as more Pokémon are seen or caught. Seeing a Pokémon will give a picture of its image, and the area in the region it lives in. Catching one will give a small bio, and reveal its weight and height in comparison with the trainer.
Many Pokémon Trainers compete in a regional Pokémon League. To qualify for league competition, a Trainer must win a number of badges from various Pokemon Gym Leaders throughout the region through Pokémon Battles by defeating the gyms' leaders.
An individual usually receives their Pokémon Trainer's license when they become or are older than 10 years old. Authorities chosen by the regional Pokémon League, usually a Pokémon expert such as Professor Oak, will allow a Trainer to choose their first Pokémon from three, which vary from region to region. Of course, those people who already have possession of a Pokémon, either as a pet or inherited through family, may eschew this process and start their journey with that Pokémon.