Dr. Riddles, known in the original Japanese version as Nazonazo Hakase, is a tall, elderly American man with a distinct and theatrical appearance. He is sixty-eight years old and is characterized by his long, gray hair and a prominent, pointed nose. His face is framed by a wizard-like mustache and beard, and he always wears a monocle over his right eye. His attire is a formal black suit and a long cape, topped with a top hat that features a large question mark on its band, a symbol that reflects his identity.

Before becoming a bookkeeper for a mamodo, Dr. Riddles lived a very different life as a royal surgeon. His career came to a tragic end when he was unable to save his own grandson during an operation. Overcome with grief and a loss of purpose, he retired from medicine and secluded himself in a remote mansion, surrounding himself with an immense library to study endlessly. Despite acquiring vast wisdom, he still felt a profound emptiness, as he had no goal to apply his knowledge.

His personality is a blend of mystery, showmanship, and deep-seated kindness. He carries himself with a perpetual, almost villainous grin and has a love for cheap magic tricks and riddles. However, his riddles are often absurdly simple and provide little practical value, serving more as a reflection of his eccentric and playful nature than any real test of intellect. Behind this theatrical exterior lies a benevolent and caring individual whose life was given new meaning by the arrival of his mamodo partner, Kido. The small, robotic-looking mamodo reminded Dr. Riddles of the grandson he had lost, and he came to see Kido as a second chance to protect and nurture a child.

Dr. Riddles enters the story as a mysterious figure known as the man who knows everything. He approaches the protagonists, Zatch and Kiyo, initially appearing as a potential rival. He battles them with Kido and his self-created team of American superheroes, the Majestic Twelve, who possess impressive but ultimately useless powers. It is soon revealed that this confrontation was not malicious; it was a test. Dr. Riddles was evaluating Zatch and Kiyo's strength and character, as his true mission was to recruit worthy mamodo pairs into an alliance to fight a greater evil. He organizes a team of mamodo and their human partners, uniting them to face the powerful Zofis and his army of ancient mamodo.

The core of Dr. Riddles' motivation is his deep affection for Kido, whose goal he dedicates himself to achieving. He vows to use all of his accumulated wisdom to help Kido become the kind king of the mamodo world. He is a strategist and a mentor, using his knowledge of the spell books and the mamodo battle to guide his allies rather than relying on his own combat prowess. His relationship with Kido is paternal and profound; Kido, in turn, has immense respect and admiration for the Doctor, and his innocent nature makes him the perfect target for Dr. Riddles's harmless pranks.

Dr. Riddles himself possesses no magical abilities, as those belong to his mamodo partner, Kido. His value in battle comes from his brilliant mind and his experience. His role is to read Kido's spell book and command him in combat. He also employs his stage magic for simple tricks and escapes. His most notable non-spell ability is his leadership and organizational skill, demonstrated when he formed the Majestic Twelve, a group of costumed heroes he personally assembled. While the Majestic Twelve are largely ineffective in a serious mamodo fight, their creation highlights Dr. Riddles's ingenuity and flair for the dramatic. It is through Kido that he unleashes his battle potential, commanding a variety of powerful offensive spells, including laser cannons, rocket punches, and deploying an army of aggressive mini-Kidos.