I recently took apart some of my sets so I could make some more mocs and this was one of the products.
At first he was a normal matoran living on spherus magna, but after he was convinced to steal a powerful mask he went into hiding. He climbed the tallest, coldest, most harsh mountain in the north and was never seen again. While there, he learned his mask power, transformation, and taught himself how to fight. He is now resistant to cold and can channel his his energy into powerful glowing attacks. He was named polaris by the matoran who claimed to see his powerful glow, which looks like a star on top of the mountain.
Also I know the toa version looks like a recolored onua. I had nothing to do with the parts so I upgraded the matoran version.