Ash Ketchum, known as Satoshi (サトシ) in Japan, is a character in the Pokémon franchise owned by Nintendo, Game Freak, and Creatures. He was the protagonist of the Pokémon anime for the first 25 seasons, as well as the protagonist of several manga series. In Japanese, the character is voiced by Rica Matsumoto. In the English dub, he was voiced by Veronica Taylor in the first eight seasons and Sarah Natochenny afterwards. Ash is a young boy who travels with various companions, aiming to fulfill his dream to become a Pokémon Master; his Pokémon lineup constantly changes over the course of the series, with its sole constant member being Pikachu, Ash's first Pokémon. Ash is loosely based on Red, the player character from the Generation I games Pokémon Red and Blue. Satoshi Tajiri, the creator of Pokémon, has stated that Ash represents the "human aspect" of the series, and that Ash reflects what he himself was like as a child.

Ash has been criticized for being stuck in a "floating timeline", as well as for his long-lasting inability to win many major Pokémon League competitions in the series. However, his longevity and persistence have also been positively received, and his character has received attention for teaching important and relatable lessons to children. Ash ultimately became Alola League Champion in Pokémon the Series: Sun & Moon – Ultra Legends, and World Champion in Pokémon Ultimate Journeys: The Series.

Due to the huge popularity, success, and longevity of the Pokémon anime series around the world since its debut, Ash has gone on to become one of the most well-known and recognizable fictional characters of all time. He is considered a pop culture icon and a figurehead character of the wave of anime in the late 1990s. He has been used extensively in merchandise for the series.

Ash was designed by Atsuko Nishida, and named after creator Satoshi Tajiri. The character was designed to represent how Tajiri was as a child, obsessed with catching bugs. During localization of both for North American audiences, the character's name was changed in the anime to "Ash Ketchum", the first name taken from one of the possible default names players could select for the player character in Pokémon Red and Blue, and the surname tying into the tagline for the series, "Gotta catch 'em all!". He is loosely based on Red, the player character of Pokémon Red and Blue.

Tajiri noted in an interview that between Japanese and US reactions to the series, Japanese consumers focused on the character Pikachu, while the US purchased more items featuring Ash and Pikachu, his Pokémon, together. He stated that he felt the character represented the human aspect of the franchise, and was thus a necessity. The character was given a rival named Gary Oak (Shigeru Okido in the Japanese version, after Tajiri's idol/mentor Shigeru Miyamoto), loosely based on Red's rival Blue. In an interview Tajiri noted the contrast between the characters' relationship in the games and anime; while in the games they were rivals, in the anime, Shigeru represented Satoshi's master. When asked if Satoshi would equal or surpass Shigeru, Tajiri replied "No! Never!" Ash's character design was initially overseen by Sayuri Ichishi, replaced by Toshiya Yamada during the Diamond & Pearl series of the anime. Ash received a redesign in the Best Wishes! series, which included larger brown irises. In the XY series, he received minor changes, such as a decrease in the size of the thunderbolt-shaped "birthmarks" on his cheeks. Ash received a major design overhaul for the Sun & Moon anime series.

In Japan, Rica Matsumoto has provided the original Japanese voice of Ash since the series' start. Matsumoto highlighted a past experience in which she recorded a message for a hospitalized child as the character, which she stated caused her to feel "more aware of the work I was putting out there." This caused her to change her approach to voicing the character. Her role has been considered highly iconic. Matsumoto voiced Ash as a kind character, and stated that she did not stray away from that portrayal in her performance, even under special circumstances. Hana Takeda briefly voiced the role in Pokémon Journeys: The Series, portraying Ash when he was a child.

For the English dubbing, Veronica Taylor provided the voice of Ash in the first eight seasons of the Pokémon anime, which was dubbed by 4Kids Entertainment. At the time of her audition, Taylor stated that the character was temporarily named Casey. After the script was translated from Japanese, the lines were adapted to fit the movements of the character's mouth (called lip flap). All the voices were recorded separately, so Taylor was the only one in the booth when she recorded her lines, which took approximately six to eight hours per episode. Taylor was often the first person to record, so she had to "imagine how the previous line will be said". A director worked with Taylor to help with interpretation of the line, as well as matching with the lip flap and voice consistency. Taylor enjoyed playing Ash because of his "low, husky voice" and "energy and excitement". Taylor was first introduced to the role via a brief voice clip from the Japanese airing. The job moved quickly, and Taylor's past acting experience allowed her to embody the role in the time allotted for recording.

Taylor commented that Ash and the other characters "loosened up" after the first ten episodes of the anime; she believed the writers were more relaxed and no longer felt the pressure of making sure everything was done correctly. Taylor commented: "I enjoy playing Ash now much more than I did in the very beginning because I can have fun with him more, and we kind of know him and can work out how he really would react. We have the classic Ash responses and things like that." Sarah Natochenny replaced Taylor in season nine when The Pokémon Company International (known at that time as Pokémon USA) took over the licensing, prompting a shift in recording studios. Natochenny has cited Matsumoto's performance as inspiration for her performance as Ash.