Kratos and Bia are the powerful bodyguards to Athena. However, they were not always the hulking behemoths they are today. They originally tried to join the Warriors, a pair of skinny, pale brothers from Kings Row. Athena turned them away, saying they lacked the physical strength of a true warrior.
Desperate to grow stronger, the pair started abusing superadine. They grew more and more muscular, but were careful not to lose their sanity and become one of the many Trolls that inhabit Skyway City. But, overtime, their addiction led them to switch to using uncut superadine.
Still remaining human, but becoming so massive and enraged that they now live only to fight, as well as serve Athena. Trying to take down Kratos or Bia alone would be a challenge. But to add insult to injury, they're almost always together
During The Olympiad the brothers were tasked with torturing Grant Miller after competition rules were broken. They beat the hero to within an inch of his life, he lived only due to his rapid healing factor.
When Athena's Island was invaded by Longbow, the brothers made their final stand against the heroes, and injected themselves with a dangerous level of superadine, which caused them to change into something resembling a "supatroll". Even still, this extra enhancement was not enough and they were defeated by the hands of the former Infiltrators.
With Athena Island crumbling down, and being far too massive and heavy, the brothers were left behind. They were assumed dead.