Bill's history is deep and his power is substantial. His motives are unerringly noble.
He is the scion, champion, protector, and last surviving member of a race from the planet Korbin. Centuries ago, the Korbinites selected him ahead of all their warriors in a brutally difficult and borderline cruel process involving trials of the body and mind, ultimately augmenting him irreversibly in a process that to date only only he has had the fortitude to survive. With the best bio-cyber-genetics Korbin had to offer, he was shaped with a frightening form, like the worst predators of Korbin. They extended his lifespan, so that by the time he finally succumbed the millennia would have seen eliminated the need for his service. They gave him incalculable strength and endurance, so much so that he would survive two planets colliding and yet be able to push them apart once more. They sharpened his faculties and senses, so that even a stray gamma ray would not escape his scrutiny. They charged him with the protection of their race: to this end, he was supplied with the sentient and intelligent starship, Scuttlebutt, roughly his equivalent in power and equipped to support his every need in the task of defending them.
The task of protecting the often ungrateful Korbinites was not an easy one, and Korbin was at one point destroyed. It was during the flight from Korbin that Bill encountered who would become his oath-brother: the ancient hero Thor. Thor wielded such incredible and unfamiliar power that Bill initially mistook him for an enemy. In their melee, Thor was separated from his enchanted hammer, Mjolnir. Created and blessed by the father of all Asgard, Odin, amongst it's vast enchantments is a decree that only those heroes who are truly worthy may wield or even lift it: until Thor encountered Bill, only he had met this criteria.
When Bill lifted Mjolnir, a rush of Odin's power surged through him, the power of Thor's birthright. He realized he could use it to save his people from the demons that destroyed Korbin and still pursued them. By chance, Odin at that point attempted to recall his son, unaware that it was Bill wielding Mjolnir. After a brief parley, Odin was so impressed with the Korbinite champion and his desperate goal of saving the Korbinites that he elected to let Bill and Thor compete for Mjolnir, an unarmed combat in which the mighty Thor was narrowly defeated. Bill, however, with his heart heavy realized he could not steal the birthright of his opponent. Stirred, the shrewd Odin used the last of the resources possible to provide him with Stormbreaker, different in form but otherwise equal to Mjolnir.
The two heroes soon discovered that they had a common enemy in demons pursuing the Korbinites, as Asgard was the next to be attacked. With their powers combined they drove back the demon threat and Bill resettled his people on New Korbin, but even as the Korbinite pariah fought doggedly against one threat or another, after a long chain and many decades of slim victories the unappreciative and seemingly cursed Korbinites were exterminated.
Bill, however, carries on as a protector of all things virtuous, wielding the enchanted war-hammer Stormbreaker and traveling with the ever faithful Scuttlebutt. In terms of physical ability, Bill's power is extraordinary. Stormbreaker, made of totally indestructible Uru metal, responds to his will absolutely, maneuvering through the air however he requires. Pulling Bill in tow it has traversed galactic distances in less than a day. It grants him the ability to sense, channel and transmute energies of almost any kind, and grants him the thunder god's birthright of controlling the weather amidst other abilities. As would be expected, as a hammer it is rivaled only by Mjolnir; whether thrown or swung, few have ever withstood a blow from it, especially with Bill's arm behind.