|Allies||Bob, Pete, his uncle and aunt|
|Affiliation||The Three Investigators|
|First Appearance||The Secret of the Terror Castle.|
|Last Appearance||The Mystery of the Cranky Collector.|
Jupiter "Jupe" Jones was an orphan, and was one of the three members of the titular detective firm, The Three Investigators, also including Bob Andrews and Peter Crenshaw; he was the First Investigator, and was considered to be their leader. He had astute deductive skills, was highly perceptive, and had a keen intellect. He often used words uncommon for anyone his age, much to the dismay of his colleague and friend, Pete. He once even confessed that due to his use of such words, he was disliked by some people, but he not could stop using those words.
He was also involved in acting when he was young, and due to his experience in acting, he could act as if he is older or younger than what he actually was, and he could impersonate people. This helped very much in getting information from suspects. His parents died when he was young, and he had been living with his aunt and uncle, Titus and Mathilda Jones, ever since. He had also formed the concepts of, and created all of, the devices for the detective firm he is a member of.
It is often implied that Jupiter is quick to start any investigating any mystery that he stumbles upon, and that nothing would be able to stop him investigating something after he starts to. This "not giving up on a mystery" attitude forces the other two boys to accompany him. Jupiter also has a secret hideout that he visits everyday