Choi Iseul is a prominent character from the Pokémon anime, first appearing as a central figure in the original series. She hails from Cerulean City, where she initially worked as a gym trainer alongside her three older sisters at the Cerulean Gym. Seeking to prove herself and escape what she perceived as the annoyance of her siblings, she declared her ambition to become the world's greatest Water-type Pokémon trainer and set out on her own journey.

Iseul has a strong-willed and assertive personality, often displaying a short temper and a no-nonsense attitude. This is evident from her first encounter with Ash Ketchum, whom she initially scolded and slapped after seeing his injured Pikachu. Despite her fiery demeanor, she possesses a deep sense of responsibility and care for Pokémon. Her decision to travel with Ash was born from a promise to repay a debt after Pikachu accidentally destroyed her bicycle, an event that has become a recurring theme in the series for introducing new female traveling companions. Throughout her journey, she frequently acted as a voice of reason for Ash, providing strategic advice during his Gym battles, though she was often frustrated by his stubbornness.

Iseul's primary motivation is to master Water-type Pokémon. As a trainer, she specializes in this type, and her team is predominantly composed of water-based species. Her notable Pokémon include her starter, a Goldeen named Conchi, which she often used for aquatic movement despite its limited effectiveness on land. Her primary battler in the early stages was a Staryu. She also owns a Golduck named Acusta, though this Pokémon is noted for having a less prominent battle record. One of her most powerful and recognizable Pokémon is Gyarados, which serves as her ace. In later appearances, particularly during a reunion in the Sun & Moon series, Iseul demonstrates her growth as a trainer by using a Mega Gyarados in battle. Another significant member of her team is a Kingler named Wangguri. This Pokémon evolved from a Krabby after coming into contact with a King's Rock, showcasing an alternative evolution path that surprised her friends. Unlike its pre-evolved form, this Kingler has a calm and sociable personality.

In the overall narrative, Iseul serves as Ash Ketchum's first female traveling companion. Her role was crucial in the early anime, providing a dynamic contrast to Ash's recklessness and helping him learn the fundamentals of being a trainer. After traveling with Ash and Brock through the Kanto and Orange Islands regions, she eventually returns to Cerulean City to take over full-time management of the Cerulean Gym when her sisters leave for an overseas trip. Over the course of her appearances, Iseul develops from a somewhat insecure girl running away from home into a confident and accomplished Gym Leader who has mastered advanced techniques like Mega Evolution. Her signature habit in official matches is calling out her Pokémon with the phrase, "Come out! My cutie!" accompanied by a gesture of kissing the Poké Ball before sending them into battle.