Hamtarō is a male golden hamster who serves as the central protagonist of his franchise. He belongs to a young girl named Laura Haruna, having moved into her home which becomes the initial setting for his many adventures. Physically, he is characterized by his orange and white fur, pink paws, a distinctive orange patch near his tail, and small black eyes. His personality is defined by a happy, energetic, and deeply curious nature, approaching each day with an enthusiasm focused on friendship and fun. He is consistently brave and selfless, often stepping into dangerous situations to help others, such as when he rescues the young hamster Penelope from a cat during a rainstorm. Despite his courage, he possesses a great deal of innocence, which often leaves him completely clueless, particularly regarding the concept of love and romance. This naivete is a core trait, as multiple female hamsters including Bijou, Sparkle, and Oshare develop crushes on him, yet he remains largely unaware and maintains a purely platonic view of their friendships.

Hamtarō's primary motivation stems from his deep loyalty to his owner, Laura, and his desire to help his friends. He becomes visibly upset when ignored by Laura and frequently rallies his group of hamster friends, known as the Ham-Hams, to solve problems, whether they involve assisting their human owners or helping one another. He often acts as the heart and inadvertent leader of the Ham-Ham Gang, emphasizing teamwork and cooperation in their many adventures. His role in the story is that of a unifying force, always ready to lend a helping hand and mobilize the group to overcome challenges. Key relationships define his journey. His best friend is Oxnard, the first hamster he met after moving, and they share a strong, brother-like bond. He has great respect for Boss, an older hamster who initially acts as the self-proclaimed leader of the group, though Hamtarō is often the one who truly brings the Ham-Hams together. The most significant dynamic is with Bijou, a French hamster who has a persistent crush on him; she often organizes dates or competitions for his attention, but due to his oblivious nature, his feelings for her remain those of a close friend. Hamtaro's development remains consistent throughout the main series, focusing on his enduring traits of optimism, loyalty, and courage as he faces serialized challenges, from reuniting lost friends to navigating the temporary dissolution of the Clubhouse. Among his notable abilities are his fearlessness in the face of danger and his talent for problem-solving, which he achieves by fostering collaboration among his friends. He communicates with a playful speech pattern, using exclamations like "Hamha!" and "kushi-kushi," and in the original Japanese version, he often ends his sentences with the unique verbal tic "nanoda".