The genetic differences between the six Toa caused them to assume new unique characteristics when their transformation was completed. Whenua become short and stocky in his build, with strong shoulders and upper arms, but relatively weak hind legs that made him the slowest runner.
Nokama grew long and sleek, able to leap great horizontal distances.
Matau's transformation seemed to have stalled before it was complete, as he continued to walk primarily on two legs. He was also the most diminutive of the Hordika, and the most greedy.
Nuju's new form was uninteresting, but his personality was most unusual. His nerves were shaky and he became the most passive and easily frightened of the group.
Vakama, predictably, was the most ill-tempered Hordika, prone to overreaction and fits of rage. He felt himself superior to his brethren in every way, but the deep evil & hate within him clouded his judgement and limited his ability to act on his feelings.
It was Onewa, exceedingly strong of body and clear of mind, who proved to be a natural leader.
The numerous deadly Rahi that inhabited Metru Nui in its darkest days made survival difficult for any and all creatures, and the Hordika found that they were best off sticking together to find & hunt food and to defend themselves. Onewa's consistent good judgement, combined with his prowess in battle, caused him to gain strength rapidly and he could feel pure power coursing through his veins. Eventually, he was able to undergo a second transformation, becoming the very first Great Hordika.
An enormous beast oozing raw physical strength, Great Hordika Onewa was not a creature to challenge, and yet, with his newfound power came no change in his demeanor. He continued to lead his fellow Hordika, but freely shared all food he gathered or caught, and demanded nothing in return but respect and loyalty.
Vakama, meanwhile, grew ever more jealous of Onewa, and irritated by the others whom he saw as increasingly weak and subservient. He turned to the mischievous Rahaga Iruini for solace. In private meetings they mocked the other Hordika and fantasized of a day when the others would be but obedient slaves to the clearly superior and more capable Vakama. Over time, the tone of these conversations became more serious, and the two actually began to devise a plan to turn Vakama's dream into a reality.
Over the following year, Vakama pretended to slowly acquiesce to Onewa's leadership and even began doing favors for the Great Hordika such as bringing him his favorite fruit. Into one of these delicious treats, Iruini secretly injected a mutated form of the Hordika venom. Upon injesting it, Onewa quickly felt a new surge of energy as the venom briefly boosted his strength as it took hold. Not long later, though, he started to become terribly disoriented, and he instructed the group to rest at a camp while he broke ranks to collect himself alone where the others would not witness his wavering condition. Vakama quietly followed a safe distance behind. Onewa became increasingly concerned about what was happening to him, and his walk turned into a frustrated jog. His eyesight began to fail and he crashed and tripped through bushes and vines, eventually collapsing to the ground in a small clearing. This is when Vakama revealed himself and what he had done. Onewa summoned the strength to come to his feet and angrily charge after the treacherous Vakama, but nearly blind and with weakening joints, he couldn't mount any form of effective attack. Vakama merely sidestepped and smiled before pouncing visciously upon his poisoned victim, brutally assaulting him and bringing him to within an inch of his life. Standing over the head of the defeated and nearly lifeless Onewa, Vakama himself underwent the dramatic transformation into a Great Hordika, while Onewa simultaneously shrunk back to normal size.
Onewa would actually recover from his physical injuries, but the mutated venom left him blind and simple-minded. From then on, the heartless Vakama would subjugate the Hordika and lead them with an iron fist, or should I say, four iron claws.