Jack "Jackie" Dio evidently has a long and sordid history. At some point, he may have worked for Silvermane, presumably using another codename and identity. During that time, Hammerhead killed Underworld’s best friend a hood known only as “Joey D”) – because Joey owed the crime lord two grand. Before he could exact revenge, Underworld was incarcerated for unknown crimes and spent about ten years in prison.
Release from Prison
Upon his release, Underworld began working for his old enemy, Hammerhead. Hammerhead was attempting to organize a criminal syndicate, allegedly to oppose the recently passed superhero registration act. His real motive, however, was to steal territory from the imprisoned Kingpin. When the villain Slyde refused to join Hammerhead’s organization, Underworld shot Slyde in the back of the head, killing him in cold blood.
Later, Underworld helped Hammerhead organize a meeting with over a dozen costumed criminals. The gathering was raided by Iron Man and S.H.I.E.L.D., who had been duped by the Kingpin into thinking that the meeting spot was a hideout being used by Captain America and his Anti-Registration Underground allies. During the ensuing battle, Underworld ambushed Hammerhead and shot him in the back with adamantium bullets. Hammerhead survived, but Underworld visited him in the hospital and revealed that he was working for the Kingpin. He was also still angry over the death of Joey D. Underworld then killed Hammerhead by putting an adamantium bullet into his brain.
- Super-Soldier Serum: Underworld possesses a variety of heightened abilities as a result of being exposed to a gaseous variant of the Super-Soldier Serum that first produced Captain America called SSS.2.
- Peak Human Strength: Underworld's physical strength has been increased to the peak of human capability. While he isn't superhuman, he is as strong as a human being can be and can lift approximately 800 lbs.
- Peak Human Speed: Underworld's running speed is also increased to the maximum of human capability and can run at a top speed of about 30 miles per hour.
- Peak Human Stamina: The serum has increased the efficiency of Underworld's musculature to the point that it produces less fatigue toxins than the musculature of most humans. He can physically exert himself at peak capacity for about 1 hour before the build up of fatigue toxins in his blood begins to impair him.
- Peak Human Durability: While Underworld still has the same physical vulnerabilities as other humans, his body is more resistant to injury and disease than most other humans.
- Peak Human Mental Process: Underworld has also been mentally enhanced by the serum, and can think as well as mentally respond at speeds which are at the pinnacle of human perfection. It is also possible that he has a photographic memory.
- Peak Human Agility: Underworld's agility, balance, and bodily coordination are also increased to levels that are beyond the natural physical limits of any Olympic athlete that has ever competed, though they don't reach superhuman levels.
- Peak Human Reflexes: Underworld's reflexes are similarly enhanced and are at the peak of human potential.
- Regenerative Healing Factor: After being shot by the police during a stand off with the Punisher Jackie was visited by the Consultant in Rykers infirmary and injected with a serum that gave him a healing factor. The full limits of his healing factor aren't known, but he can rapidly regenerate damaged bodily tissues much faster and more extensively than any normal human. For example, he can fully heal from multiple gunshot wounds within a matter of moments. Due to the efficiency of Underworld's healing factor, probably also renders him immune or more resistant to disease, drugs, and toxins and suppresses his ageing process, as with Deadpool and Wolverine. It is unknown if he's able to regrow lost or severed limbs, but he was shown being able to regrow his teeth, having lost them in his encounters with his super-powered younger brother, Mr.Pain, and Punisher.
- Hand to Hand Combat: Underworld is a formidable hand to hand combatant, particularly when using street fighting techniques. Also, due at least to some degree of his equipment, Underworld is also an expert marksman.
- Tracker: Underworld seems to be able to track others very well, which was evidenced when he was able to track both his brother Vince, and Hammerhead.
- Special Sunglasses: Underworld possesses a pair of sunglasses that are composed of an extremely durable, though unidentified, substance. The glasses enable him to see in the dark perfectly via infrared imaging. Through some unexplained technology, the glasses are connected to the bullets that he fires from his gun. The glasses lock onto a target and once he fires the bullets, they'll follow a target no matter what the target does to get away, even if he/she runs around corners.
- Titanium Lined Coat: Underworld almost always wears a long, calf-length coat that's lined with titanium, rendering most of his body highly resistant to most forms of conventional physical attack.
Pistols: Underworld carries a pair of advanced pistols capable of firing adamantium rounds.
- When Underworld first appears, Hammerhead introduces him as "an old kid who just got out of stir and re-entered a very new game..." Other comments in the issue suggest that Underworld was once some other criminal.
- 6 appearance(s) of Jack Dio (Earth-616)
- 3 appearance(s) in handbook(s) of Jack Dio (Earth-616)
- 1 mention(s) in handbook(s) of Jack Dio (Earth-616)
- 7 image(s) of Jack Dio (Earth-616)