* Conor Broekhart: The protagonist, a 15-year-old boy from Dublin, Ireland, who discovers he is a member of an ancient alien race known as the Airmen and must travel to Jupiter to save humanity.
* Lara: A mysterious teenage girl who appears in Conor's dreams and helps him connect with his Airman abilities.
* Ethan Skulduggery: A former Airman who helps Conor hone his skills and prepares him for his mission to Jupiter.
* Dr. Ichabod Spallanzani: A brilliant scientist and member of the Airmen, who helps Conor understand the history and technology of the Airmen.
* Commander Vilo Versh: The leader of the Airmen and Conor's main antagonist.
* Milo Mindbender: A powerful enemy of the Airmen and Conor, who seeks to use their technology for his own nefarious purposes.
* The Earthbound: A group of humans who are working with the Airmen to save the Earth from an impending disaster.