Belial-There was a Tohunga named Ngaro, he didn't belong to a village.
He was jealous of the Toa's power, and he wanted to by one too.
Makuta saw this, and sent a servant to offer him a proposition, Makuta
would give Ngaro the power to be a Toa, but he had to destroy the other
Toa, Ngaro hesitantly excepted, so Makuta gave him the power to absorb
some of the Toa.   So when Ngaro came to the Toa, he absorbed Kopaka
and Onua, he soon crafted a body and a sword/gun out of their parts.
Makuta also granted him a special infected mask, keeping his free-will,
but directly connecting him to Makuta's power.   He was later killed by
Supreme Tahu using energy from all of the Toa.   Kopaka and Onua
returned briefly, but were soon captured by Makuta.