The Captain was an ordinary human from Brooklyn. One night, while on a bender in the streets of Brooklyn, two aliens of unknown origin named Spa-Fon and Squa-Tront, came across the man who was to become the Captain. They granted to him the "Messianic Sidda-Complex," the "the Heartstar of the space between galaxies." He was tasked with using his newfound power and glory to "make this nightmarish land of 'Brooklyn' a better place." He then used his newly-gained superhuman powers to beat up the aliens because he "thought when you hit leprechauns on the head they turned into gold coins." Finding that this was untrue, he bent over with the intent of robbing them, and instead vomited onto his extraterrestrial benefactors.
Mayor Story Arcs
Meeting another Captain
The Captain has also revealed that he has tried using almost every codename imaginable starting with 'Captain'. Each time he used one, he discovered it was already IN use, leading him to finally choose a name he has only said was 'Captain' and some expletive, which was filthy enough that when Captain America heard it, he punched the Captain in the face. Subsequently, he decided to just go by 'The Captain'.
With the other members of Nextwave, the Captain is on the run from Dirk Anger, head of H.A.T.E. (Highest Anti-Terrorism Effort) the organization that first brought them together. Beyond that, anything else that might flesh out The Captain's character is purely speculative. He seems to have a strong rapport and perhaps even some romantic inclinations towards his teammate Bloodstone.
Also, there is one flashback in the series that shows The Captain as a child, walking into his room to find his mother sitting there shining a flashlight for dramatic effect upon his favorite teddy bear which she has hung from a noose. This likely screwed him up in the head. In this flash back, his younger self was still wearing the same star-emblazoned t-shirt. If that actually means anything, or whether this was just done so the reader would immediately know who they were seeing as a child, is unclear.
The extent of the Captain's power is, at this point, unknown. The Captain possesses what are by his description a "generic set of special super hero abilities" as a result of possessing the Heartstar.
He has demonstrated the ability to fly as well as extreme super strength allowing him to hurt the dragon Fin Fang Foom, breaking and even tearing off one of Foom's fingers. He also possesses a degree of invulnerability and superhuman sight.
The Captain's powers are based on the so-called "messianic Siddha-complex".
Scenes showing him as a wielder of the the Unipower, the roving power that causes individuals to become ' Captain Universe', were caused by mental hallucinations to confront the members of Nextwave with their greatest fears.