Q Junior was the son of Q and Miss Q. He was conceived during the Q Civil War as a way to help restore the status quo of the Q Continuum and end the conflict. Shortly after his birth, Captain Kathryn Janeway agreed to be his godmother, based on the fact that she had supported and encouraged Q during the civil war. (VOY: "The Q and the Grey")
Though his parents had great hopes for their child as the "savior" of the Continuum, the high expectations had a dramatic effect on the young child's attitude. Junior became obnoxious, spoiled and disruptive and lacked the kind of qualities that could inspire the much needed peace and compassion in the Continuum.
Frustrated with his son, Q sent him to the USS Voyager, hoping that Janeway's "vaunted Starfleet ideals" would rub off on the boy. However, Junior became even more disruptive, such as propelling Voyager into the path of three Borg cubes, fusing Neelix's mouth shut when he tried to help him out and removing Seven of Nine's clothing to stare at her naked body. Fed up with his son's misbehavior, and inspired by Janeway's suggestion that he make his son realize that his actions would have consequences, Q stripped him of his powers and left him on Voyager for a week under the guidance of Captain Janeway. If he did not behave himself, his father warned him that he would not hesitate to turn him into an Oprelian amoeba.
Initially, Junior's lessons on Voyager were a dismal failure. He plagiarized an essay on the Q Continuum from Icheb and secretly reprogrammed a holodeck simulation so that the solution could be achieved more easily. However, when Janeway threatened to cut off his lessons and return him to his father, Junior resolved to behave more appropriately. He became fast friends with Icheb, whom he nicknamed "Itchy" – and who in turn nicknamed him "Q-Ball" – and finally began putting some effort in his assignments and his character.
His father was not very satisfied with Junior, however, as he felt that he did not live up to what was expected of him. Angry that apparently nothing he did was good enough for his father, Junior stole the Delta Flyer and took Icheb with him to a joyride to the Clevari system. During his stunt Icheb was seriously injured when a Chokuzan vessel opened fire on the Flyer. The Doctor was unable to treat Icheb without knowing more about the weapon that had caused his injuries. Junior realized that the only option left for him was to return to the alien ship and surrender in exchange for information about the weapon they used. When the Chokuzan decided to blame and punish Janeway as guardian, Junior defended her and insisted that only he be punished for his misdeeds. After this selfless act the truth finally came out: the whole incident was a set-up by Q to test his son's character.
The Continuum, however, was not impressed by Junior's progress, and initially re-sentenced him to become an amoeba. After some consideration on Junior's self-sacrifice for Janeway, the Continuum changed his sentence to remain in Human form, but stripped of his powers. They only acquiesced when Q vowed to stay with him and take responsibility for his son for all of eternity.
Q Junior was portrayed by the two infant brothers Brett and Nolan Donahue. Their costume was sold off on the It's A Wrap! sale and auction on eBay.  They filmed their scene on Monday 16 September 1996 on Paramount Stage 8 and are listed as "2 Babies (Donahue Twins)" on the call sheet.
In the episode "Q2", Junior was played by Keegan de Lancie, who is the real-life son of Q-actor John de Lancie. The older de Lancie once remembered, "My agents called me and said, 'By the way, I don't know if you know this, but they are casting for the character of your son. Do you want me to submit Keegan?' 'I don't know. Let me ask him.' I said, 'Keegan, would you like to be in Star Trek? Obviously, you have to audition for it.' So he went in, auditioned and got past station number one. He had to audition two or three times and I believe they hired him because he did a really great job. I had nothing to do with it." (Star Trek Magazine issue 168, p. 50)
His name came from dialog, where he was referred to as "junior" by his father. In the script, he is identified as "Q2", which was the name previously given to the character played by Corbin Bernsen in "Deja Q". (Star Trek Encyclopedia (4th ed., vol. 2, p. 190))
In the Q Continuum novel trilogy, Junior, while still an infant, visits the USS Enterprise-E with his parents when Q attempts to halt a Federation experiment to penetrate the galactic barrier using an artificial wormhole. During their time on the ship, Junior's mother reflects on her own fears about motherhood, but is slightly consoled by Doctor Beverly Crusher. Junior is briefly captured by an insane Betazoid scientist who has been enhanced by the barrier's psychic power and subsequently "possessed" by Q's old enemy/mentor 0, the scientist intending to test Junior's capabilities in various ways, but he is released thanks to his mother. In the novel, he is referred to exclusively as q, in lowercase.
In The Eternal Tide, Q works with Kes to resurrect Admiral Janeway after she was assimilated by the Borg and killed in the battle to save Earth when he becomes convinced that she is needed to stop a threat that was stopped by Voyager in the timeline before Janeway's other self changed history. He is subsequently forced to sacrifice himself to stop the Omega Continuum whose release could annihilate the entire universe, crediting Janeway with inspiring his decision.
In Star Trek Online Junior took on the role of his father (even donning the robes worn in "Encounter at Farpoint"), interacting with the player in a mission where he sends them back in time to the Battle of Wolf 359 to prevent the death of Benjamin Sisko at the hands of an unknown enemy, which sent a number of the Borg back in time to the USS Saratoga. Junior also features prominently at Earth Spacedock and Qo'noS during the yearly anniversary celebrations of the game and the yearly winter holiday celebrations. He took credit for changing the Earth Spacedock into the design seen in the films and Star Trek: The Next Generation from the previous design that had been similar to the one seen in Star Trek. He also maintains the Captain's Table, a cross-faction neutral ground space station accessible to lifetime subscribers.