Ash Ketchum with Pikachu.

Ash Ketchum (Japanese: サトシ Satoshi) is the main character of both the Pokémon anime and The Electric Tale of Pikachu manga, and is believed to be based on the protagonist of the first generation Pokémon games.

He shares his Japanese name—which can be taken to mean "wisdom" or "reason" (智)—with the creator of the Pokémon franchise, Satoshi Tajiri. His English surname is a pun of the original English motto, Gotta catch 'em all!

Ash's main goal in life, as described in the first episode, is to be the world's greatest Pokémon Master.

One particular characteristic about Ash that has not changed over the course of the series, aside from his determination and his passion for raising and training Pokémon, is that he is incredibly selfless. He will often (and this has happened for just about every one of his Pokémon) go to extraordinary lengths to earn a Pokémon's trust and respect; and he will often go out of his way to better understand a Pokémon that he sees as troubled. He is also very fair-minded and trusting, a true testament to his good-natured character.

Ash is shown to have a strong sense of justice, especially when it comes to Pokémon. If a Pokémon is in trouble he will go out of his way to help them, even if he has no prior connection to them. If they are the cause of trouble, he will stop them, and then try to understand them, with almost all such occasions being a case of the Pokémon (or their trainer or friend(s)) having a problem which can't be resolved normally. In those cases, he will selflessly volunteer to help them. Should the problem be caused by a person, such as a Team Rocket, Pokémon thieves, hunters or poachers, Ash resolves to do anything in his power to stop them.

Despite this, and previous dealings with evil organizations, Ash has retained remarkably optimistic and naïve outlook, a trait his companions seem to share. He is quick to praise and has an unshakable trust in both his Pokémon and his friends. He is unable to see through the disguises of the Team Rocket trio, and will try to see the best in everyone and everything. An example would be Team Rocket's frequent 'sudden appearance' that coincidentally coincides with their needs at that time, and Ash never questioning it until it is too late. Another example would be how he easily praises Clemont for his 'genius' inventions, no matter their high failure rate, and the near inevitable explosion, or Cilan for his other varied 'connoisseur abilities,' even if they are ridiculous. Furthermore, even though almost all of his friends have large dreams, Ash fully supports them and has never doubted their ability to accomplish them, possibly due to his own highly ambitious goal. He also encourages Pokémon to do the best they can, even if they aren't his own, and has even helped train wild Pokémon.

In the Original series, though Ash actively took part in battles, he was rarely seen independently training his Pokémon. However, since the Advanced Generation series, Ash is shown to train more noticeably, having mock battles with his friends and focusing on moves, techniques and strategies with his Pokémon. A noticeable trait is his willingness to learn from both his victories and defeats in battle. For example, after winning in a Gym battle against Winona in a Sky High Gym Battle! and witnessing her Pokémon's powerful Aerial Ace, Ash was motivated to have his Swellow learn it, which it did during Pokéblock, Stock, and 'Berry and Lessons in Lilycove!. Even after he lost a battle, and witnessing a powerful Ice Punch, as seen in Short and To the Punch!, Ash was inspired to teach his Buizel it. He even believes in using serious battles as an opportunity to help train the move, even if he loses, like during the Double Battle in What You Seed is What You Get, when he was trying to teach Treecko Bullet Seed.

In the beginning, Ash had a bit of an inferiority complex, as well as some form of personal pride, most likely stemming from his rivalry with Gary Oak. As a result, he had some bad habits, like shamelessly boasting his own skill if he were ever on a winning streak, and easily getting mad if he were personally insulted, as seen in The Path to the Pokémon League. Ash even used to call foul on things that were perfectly legal, like Giselle's Cubone using a bone in The School of Hard Knocks, or Blaine's use of the lava in Volcanic Panic. He even locked himself up in his room and sulked after losing to Ritchie, though he got over it after being scolded by Misty in Friends to the End. Fortunately, during his journey, Ash has gotten over his complex and is now easily accepting of criticism to his own skill, though he still gets upset if his Pokémon is insulted or degraded. This was actually what lead to the source of conflict between Ash and Paul in the Diamond & Pearl series.

In most episodes of the anime, especially those during the Johto League saga, Ash befriends someone who will influence him and cause him to strive to become a better Trainer. Although he is not a dependent individual, he is still young and has learned to make his way relying on his friends, particularly the maternal skills of Brock. The honor of "best friend" is usually reserved for Pikachu but Ash has come to see his closest human friends in the same light over time; using the term for Misty and Brock in Gotta Catch Ya Later! as well as May and Max in Battling the Enemy Within.