Dr. Riddles (called Professor Riddle in the original) 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," although he is clearly exaggerating. 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 negative.