Kido (called Kid in the original and spelled Kedo in the VIZ manga translation) is a lanky child mamodo who wears a blue jumpsuit with a K on it. He is partly robotic, which is shown in his various spells which involve weapons and changing the size of his body part. His spell power also happens to be machinery. Personality-wise, he is childish, cocky,and very gullible, showcased by a common scene in which Kido explains something with a lie Dr. Riddles had previously made up, and is utterly shocked when Dr. Riddles revealed he had been "kidding". Kid is shown to be easily scared, though he has grown considerably brave in the various battles he had encountered with Dr. Riddles.
Despite it all, Kido is very loyal to Dr. Riddles, going as far as to sacrifice himself to protect him, Kanchomé, and Parco Folgore in battle from Belgim E.O. He has great admiration and respect for Dr. Riddles and their relationship is viewed as that of a father and a son.
Kido appears again to aid Zatch Bell in his battle against Clear, using his strongest spell, "Mikoruo Shin Zegaruga" to destroy the fragments of Clear's severed tail, telling Zatch not to lose focus. He is later seen in the library with Zaruchim, Sugino, Momon, Zabas, Robnos, and Furigaro.
Kido is voiced by Brianne Siddall in the English version and by Akemi Okamura in the Japanese original.
Dr. Riddles is a tall, old American man with a prominent mustache, a top hat with a floating question mark above it, a monocle and fancy black clothing. He often claims to be the "mysterious professor who knows all." While he is clearly exaggerating, it may not be far from the truth, since he is one of the users of the Answer Talker ability. A frequent scene between him and Kido shows Kido explaining something that Dr. Riddles had told him earlier, only for Riddles to say he was "kidding", which causes Kido's expression to become shocked and photo negative.
Dr. Riddles is a fun and easy-going man that likes to joke about. However, he can be serious when he wants to and has a vast amount of knowledge, as shown when he teaches Kido the importance of light. Dr. Riddles is also shown to be very wise, teaching Kido many lessons about life that Kido is shown to be thankful about.
He first met Kido when Kido visited his library-of-a-house. Dr. Riddles ended up in seclusion in that house, reading many books because of a failed surgery on a child (grandson in the original version) as a doctor, which could explain his purpose for having his answer talker. He quit that job in shame, but felt more pride in purpose with Kido's help. Dr. Riddles first told Kido, when the mamodo asked him, that he was a person who knew nothing. He manages to read the spell book that Kido had presented him with and an excited Kido tells him to go outside so that he could be made the mamodo king, adding that it would be a waste if Dr. Riddles doesn't, since he knew so much.
In the battle with the Ancient Mamodo in South America, their final battle was with Belgim E.O., unlocking a new spell, Mikor Ma Zegaruga. After the battle, Dr Riddles was still upset and grieving over Kido. But when Kanchomé and Parco Folgore came around to cheer him up, he reflected about all his happy moments he had and began to embraced it, and no longer feels alone as Kido's spirit will linger around him.
Even though Kido's book is burned, Dr. Riddles continues to accompany the other mamodo teams, and is the primary source of information throughout the series afterward, supplying Zatch and Kiyo with data regarding Maestro and Faudo.
In the King Festival arc, after defeating Clear Note and Vino, Dr. Riddles adopts the baby Vino as a son.
Dr. Riddles is voiced by Quinton Flynn in the English version and by Rokuro Naya in the original. In the Youtube dub he will be voiced by Chris Bastin.
Dr. Riddles and Kid's relationship resembles that of a father and son and the duo are very close. Kido, before being sent back to the mamodo world, states that Dr. Riddles is his king. Thus, Dr. Riddles is shown to be very depressed after the loss of Kido, but is cheered up when Folgore and Kanchome visit him.
Since most of Kido's spell require distance to work effectively, Dr. Riddles usually takes advantage of Kido's robotic body. Kido will stand there and take a few hits while putting distance between him and his opponent. Eventually, Kido fires several shots ending the match. Using this plan they burned quite a few books.
Dr. Riddles leads a league of American superheroes called the Majestic Twelve. They are seen at various points in the series, though they are generally little more than support characters. The members are Lightning Eye, Rocket Foot, Flying Beat, Second Sight, Dinosaur Arm, Future Wonder, Psychic Jungle, Fire Elbow, Lady Susan, Blizzard Thing, Tremor Mole, and Telepathy Radar.
In the original, Telepathy Radar is voiced by Toshinobu Iida, Wonderful to the Future and Blizzard Thing by Jun Azumi, Second Sight by Kazuhiko Nishimatsu, Psycho Jungle by Satoshi Tsuruoka, Dinosaur Arm by Gou Shinomiya, and Big Boing by Ai Nagano. In the English dub Lady Susan is voiced by Michelle Ruff.
Dr. Riddles constantly teases Kido and others by saying "Just Kidding" or "Not Really".
It is a common gag in the series that Dr. Riddles does not use logic. Instead of explaining himself, he answers all questionings of his logic by saying "I am Dr. Riddles the marvelous doctor that knows everything."
Lady Susan is the only member of the Majestic Twelve that Makoto Raiku says does not need help from his fans to come up with ideas for a new appearance.
They are the first couple to use a "Ma" class attack.
It is worth noting, however, that Tia and Megumi Ooumi were the first to use a "Ma" class spell, Ma Seshield, however Kido and Dr. Riddles were the first to use a "Ma" class attack.