Hamtaro is a male hamster and the central protagonist of his franchise. He is owned by a young girl named Laura Haruna and lives in a small cage in her room, from which he ventures out on daily adventures. Physically, he is characterized by his orange and white fur, pink paws, a distinctive orange patch near his tail, and black eyes. His speech includes playful exclamations such as Hamha! in various language versions.

In terms of personality, Hamtaro is defined by a happy, energetic, and endlessly curious nature. He approaches each day with a focus on friendship and fun, embodying unwavering optimism and a steadfast sense of camaraderie. He is deeply kind-hearted, selfless, and always ready to lend a helping hand to anyone in need, whether a fellow hamster or a human. This selflessness is paired with considerable courage, as he does not hesitate to confront danger to protect others, famously rescuing his friend Penelope from a fierce cat early in the series. Despite his bravery, Hamtaro retains an innocent and naive worldview, which most notably leaves him completely oblivious to the concept of romantic love. Several female hamsters, including Bijou, Sparkle, Lapis, and Oshare, develop crushes on him, but he rarely reciprocates or even acknowledges their feelings, maintaining purely platonic friendships.

Hamtaro's primary motivation is the happiness and well-being of his friends and owner. His strong emotional bond with Laura is a core aspect of his character, and he becomes very upset or jealous when he feels ignored by her. He often rallies his friends to help with her problems, demonstrating deep loyalty. His role in the story is that of an inadvertent leader and the heart of the Ham-Ham gang. While a hamster named Boss is the self-proclaimed leader, it is Hamtaro's magnetic personality and proactive nature that truly unites the group and mobilizes them to solve problems and go on adventures from their central meeting place, the Ham-Ham Clubhouse.

His key relationships shape much of his story. His closest friend is Oxnard, the first hamster he met after moving to a new home, forming a brother-like bond with him. He looks up to Boss, viewing him as an older and wiser figure, and remains unaware of Boss's jealousy over Bijou's affections for him. The most significant relationship in his life is with Bijou, a female hamster from France who has a persistent and obvious crush on him. Despite her efforts, which include going on dates with him, Hamtaro remains clueless about her romantic intentions and cares for her only as a very close friend. Development for Hamtaro comes through the serialized challenges he faces, such as reuniting lost siblings or navigating the temporary dissolution of the Ham-Ham clubhouse, which reinforce his traits of optimism and loyalty without fundamentally altering his core personality. His notable abilities include bravery in the face of danger, strong problem-solving skills that rely on teamwork, and a talent for learning and using Ham-Chat, the unique language of the hamsters. While his portrayal is largely consistent across the main anime series, alternative manga adaptations present different versions of his character, such as one where he is territorial and marries a hamster named Momo, or another where he is romantically attached to his human owner.