Mexus

Mexus is a Po-Matoran who gained robotic parts after a serious injury.

Old Village
Mexus was once a normal Po-Matoran living in a humble village. Eventually, he became adventureous, and found a volcano. When he went inside the dormant volcano, he found something that accidentely activated an eruption, which nearly destroyed the village. Before the volcano erupted, the village dug a moat using their Toa of Earth and Stone, and they sent the lava into the ocean. He was then sent to Karzahni to be fixed.

Karzahni and Immortal Followers
After he was sent to Karzahni, he got "repaired." He received a Nynrah Ghostblaster, but Karzahni failed to do the rest, and ended up losing his mask and cutting off his right arm. He then went into a coma-like state due to the fact that he had no Kanohi on.

Mexus then awakened in a huge fortress and noticed he had another Kanohi, a robotic arm, and wings. He was then told of the Immortal Followers and wanted to join. He did, and acted as the team's spy, since he could go places easier than Toa could.