The Pokemon

Pokémon (abbreviated from Pocket Monsters (ポケットモンスター, Poketto Monsutā^?) in Japan) is an ongoing Japanese animated series, which has since been adapted for the North American and European television market. It is somewhat based on the Pokémon video game series and a part of the Pokémon franchise.

Originally a single series, Pokémon, it has since been made into three series, including Pokémon: Advanced Generation and subsequently Pokémon Diamond & Pearl, which continue the story of Pokémon, while its spin-off Pokémon Chronicles or, as it is known in Japan, Pokémon Sunday (formerly Shūkan Pokémon Hōsōkyoku) is a series of stories revolving around some of the recurring characters.

The first series tells the story of Ash Ketchum (known as Satoshi in the Japanese version, he is named after Pokémon's creator, Satoshi Tajiri), his friends, and his quest to become a Pokémon Master, as well as their quests. However, unlike in the video games, he is given a Pikachu as his first Pokémon under unusual circumstances. Much of the series focuses on the friendship between Ash, Pikachu, Misty, Brock, May, Max, Tracey, Dawn and the various Pokémon and Trainers along the way. Joining Ash on his adventures are Brock (known as Takeshi in Japan) who wants to become the world's best Pokémon breeder and Misty (Kasumi in Japan) who wants to be a water Pokémon trainer (Brock and Misty were gym leaders in the original Pokémon game, and were in the anime too but were able to travel with Ash due to different circumstances).

The other two series continue to follow the adventures of Ash and his friends. However, starting with the Advanced Generation series a new main character named May (Haruka in Japan) travels with Ash, Brock and also her little brother Max (Masato in Japan) through the Hoenn region replacing Misty, and competes in Pokémon Contests, which are set up in a similar manner to Pokémon Gyms (many throughout the region, and ending with a large tournament), although immensely different.

Throughout the run of the show the subject matter changes. In the original series, the show is more comical and whimsical (light and airy). It uses "goofy" humor (or "cute" humor when it comes to Pikachu, who does wacky things in between important scenes). In the Advanced Generation series as Ash becomes more of a mature and leader-type character, the main course of the show becomes more serious, as it deals with love and death, and its previous comical nature (for the most part) changes into comic relief, attributed mostly to Team Rocket and Brock's love of girls, though the Diamond and Pearl series seems to have returned to using the original comical nature (mostly Ash being the straight man to his Pokémon's antics and Dawn taking the role of the naive beginner).

Source : http://en.wikipedia.org/wiki/Pok%C3%A9mon_(anime)