Jack was a subject in a government program named project Next Men. The members of the project had been kept in a government facility in huge metal chambers. While in these chambers they were immersed in The Greenery, a virtual reality. The subjects perceived that they were in an ideal world. For the most part this simulated world was peaceful and idyllic. However, ever so often they would be attacked by war machines without notice. They were able to generate weapons and armory to ward off these attacks. During this time Jack developed Super Powers; he became impossibly strong. Jack was the first to wake up in the metal chamber and discover that they were really in a government facility. He and the other survivors of the project escaped from the government facility.
Based on the comic books that Danny had been reading they were given superhero identities, Jack became Brawn.
Jack was created by John Byrne as a member of the Next Men. Jack's mutant ability is his super-strength; this type of strong man is a staple of many superhero teams. Jack's character would be considered a flawed version of the strong man archetype. What makes Jack's character special is that he is unable to control his abilities. He has killed many people and worries that he will harm the ones he cares about, in particular his love interest Jasmine.
Jack was first depicted as a man with super-strenth but limited intelligence. While he is concerned about the ones he loves, he had very little remorse for causing the death of those that would try to harm him. He was shown as a man of action and one who will protect those that he cares for, even at great risk to himself.
He wears a restraining harness to improve his ability to control his strength. Since then he has experienced a religious revelation. He is trying to atone for his sins, and he remorseful for the deaths that he has caused.
Major Story Arcs
During the shutdown of the Next Men Project by Senator Hilltop. The Senator was doing so to hide his involvement in the project.
Having been raised in The Greenery, a virtual world for educating and training the team, the Next Men were very naive about the real-world. They work with Antonia's and her boss, Control, to prepare for real world missions. During this time Jack takes on the code name of Brawn.
One of their first missions they embark upon is to battle the similarly created Russian mutant team. During this time, Danny leaves on his own to search for his birth mother. He finds his half sister, birth mother and the real identity of his father. Danny and his half sister, Chrissy, went to New York.
The team re-unites in New York and emulates the superhero teams of the comic books that Danny reads. This attracts attention from the law, and the team is arrested for the crimes committed during the escape from the Next Men Project's government facility. Jack and the team escape and go underground. During this time Jack has a religious revelation.
In the 2010 IDW published mini-series, Jack as a relatively small role. It is clear that he has maintained and deep faith and has repaid his debt to society.