Cilan is a former Gym Leader of the Striaton City Gym in the Unova region, where he specialized in Grass-type Pokémon. He is distinguished by his green hair and eyes, and typically wears a formal black waistcoat with a green bow tie that reflects his elemental specialty. Alongside his two brothers, Chili and Cress, he was one of the triplets who ran the Gym, teaching new Trainers about type matchups. He officially holds the title of A-class Pokémon Connoisseur, a profession that involves evaluating the compatibility and bond between a Trainer and their Pokémon.

In terms of personality, Cilan is highly eccentric, energetic, and cheerful, with a deep appreciation for the intricacies of daily life. He is known for his rapid-fire speech, often sharing specialized knowledge on a wide array of subjects, from cooking to detective work. This habit leads him to adopt various alter egos, such as Detective Connoisseur or Science Connoisseur, accompanied by his signature phrase declaring that it is evaluation time. While he is generally optimistic and composed, he possesses a notable fear of the Pokémon Purrloin, stemming from a childhood incident where he was attacked by one.

Cilan’s primary motivation is to grow and refine his skills as a Pokémon Connoisseur. Initially confined to his duties at the Gym, he decided to travel with the young Trainer Ash Ketchum and his companion Iris after Ash defeated him in a Gym battle. Impressed by Ash's unique battling style and the bond he shared with his Pokémon, Cilan chose to leave the Gym in the care of his brothers to experience different people, places, and Pokémon firsthand. His role in the story during the Black and White series is that of a navigator, guide, and cook for the group, providing logistical support and culinary expertise. He is proficient in preparing meals for both humans and Pokémon.

Key relationships define much of his journey. He shares a close bond with his brothers, Chili and Cress, though he often acts as the more level-headed mediator. He develops a friendly rivalry with the aspiring Connoisseur Burgundy, who begrudgingly acknowledges his superior skills. During his travels, Cilan also forms a mutual respect with Brock, a former traveling companion of Ash who shares his passion for cooking and Pokémon care. When they finally meet, their similarities as former first-Gym Leaders and caretakers are immediately apparent. Cilan also interacts with other prominent characters; he battles Dawn in a tag battle, helps Clemont rescue his sister Bonnie in Kalos, and reunites with Ash and Iris in the special episode Pokémon: To Be a Pokémon Master years after their original journey ended.

Throughout the series, Cilan demonstrates notable development and a wide array of abilities. Beyond his battling skills as a Gym Leader, he is an expert in numerous fields, earning him nicknames like Metro Connoisseur for his encyclopedic knowledge of subways and trains. He is also a capable detective and an excellent angler. His team of Pokémon reflects his analytical nature, primarily featuring his partner Pansage, a Dwebble that evolves into Crustle, and a Stunfisk. Cilan is an empiricist who believes in learning through observation and direct experience. As he travels, he becomes more open-minded, using his evaluating skills not just for Pokémon, but to solve problems and help people, solidifying his reputation as one of the most intelligent and multifaceted characters in the anime.