Jack Power is the son and third child of Margaret Power and James Power, an inventor who once made a device which (unbeknown to him) could destroy large parts of the universe. The alien race known as the Snarks came looking for the device and thus came into conflict with the Power kids, whom moments before had received amazing powers from Whitey, an alien who died trying to warn the Power family of the nearing danger of the Snarks. Jack was given the power of body density, which meant turning into cloud-form, and shrinking to small sizes, while his density stayed the same. His siblings also gained super powers: Alex could control gravity, Julie could fly and Katie could disintegrate matter and then fire energy balls. Jack adopted the code-name Mass-Master. Although they four of them now had amazing powers, they could not stop the Snarks from kidnapping their parents and taking them of into space for further study of the humans. All seemed lost until the smart-ship (named Friday) of the now dead alien Whitey told the Power kids he could follow the Snarks and try helping them rescue their parents. The foursome went of to outer space, in hot pursuit of the Snarks. After an intense battle the Power kids found their parents on the Snarks mother-ship, where able to save them and flee the forces of the Snarks. After-wards, Jack's parents didn't have any memory of the Snarks or their kidnapping. The four siblings decided to keep their powers a secret to their parents and the world, and thus Power Pack was born, world's youngest superhero team.
Jack Power was created by writer Louise Simonson and artist June Brigman and first appeared in Power Pack #1 (1984).
Mayor Story Arcs
Power Pack soon established itself as a young superheroes team. They had their own costumes and often teamed-up with other heroes, working with larger superhero teams, like the X-men and the Fantastic Four. The team even, much to Jack's delight, became a trusted sight for the amazing Spider-man. This had been Jack's hero for as long as he could remember. Early in their careers, the team (and especially Jack) befriended Franklin Richards, who came looking for the team after he had precognitive dreams of Power Pack getting attacked by the Snark prince Jackal. These dreams turned out to be a reality when the team was in fact attacked by the Jackal. Power Pack, aided by Franklin, fought the Jackal in a lengthy battle and won. After this, the team accepted Franklin as a member of the team, codenamed Tattletale.
While Power Pack was doing battle on the Snark planet, the team went through their first 'power switch'. The team noticed that they could change powers at will, and also had a more then uncanny ability to heal faster then any normal human could. Team members could 'trade' their own power for one of their brother's or sister's. Jack gained Alex's old power, the gravity power. He could now make himself and other people or objects absolutely weightless. He named himself Counterweight and developed a 'posi-gee' punch, where he would hit an enemy with full gravity on. At the next switch, he came close to killing the menace named Maraud when he gained the disintegration power. Maraud had feared him, knowing that he could unleash the full destructive terror of the powers. Jack noticed at this point that he should be more careful when using his powers on other people. The next time the team switched powers, Jack got his density power back. He and his brother and sisters went on to battle many more menaces like the supernatural Bogeyman, but also more earthly subjects as drugs-dealers and robbers.
In between and the 2000 mini-series
After many, many adventures the Power Pack team decided to take it more easy and start living their normal lives again. This worked out for most of the time, except when Jack's oldest brother Alex briefly returned to the superhero life, aiding the New Warriors. He borrowed all of the team's powers, making Alex stronger then ever. Soon after this, peace returned to the Power's house. Jack was attending school and seemed to live the good life, a normal life whenever he could, and also a little help from his powers whenever necessary . To protect their identities Jack and his brother and sisters now whore masks whenever they appeared as Power Pack. The team had to return to their old alter-ego's again when the Snarks attacked their home. A battle was fought but the kids managed to defeat them once again and save the day.
Jack and Alex where invited for the birthday party of Franklin Richards. During this time, Jack's older brother Alex was invited to join Mr. Fantastic's new Future Foundation, a group of some of the best young minds. He accepted. Jack and Alex also fought alongside the Thing and Human Torch when the Baxter Building was invaded from the Negative Zone. He was there when Johny Storm, aka the Human Torch seemingly sacrificed his life in order to stop the invading army from the Negative Zone to reach earth. Alex is now a member of the team that replaces the Fantastic Four after the Human Torch's death, named the Future Foundation.
Jack still lives happily at his home with his parents, his brother and sisters Katie and the recently returned sister Julie.
He is an empowered human who originally gained the ability to alter his density and mass. He could originally only become a cloud, but later found out how to shrink. He has swapped powers with his sibling before, usually due to unsuccessful power transfusions. First he got the gravity power then he got the energy power.