"Darkness"

Darkness was The Shadowed One's own "shadow", always lurking nearby, waiting for The Shadowed One to make just one mistake - as soon as he did, Darkness would descend, kill him and take his place as ruler of the Dark Hunters. Until then, he had only been occasionally seen disciplining weak Hunters to keep his skills sharp.

Dark Mirror
In the Toa Empire, Darkness was a member of Pohatu's resistance team and was able to gather all of the Dark Hunters in Metru Nui to join in the final assault against Tuyet. In the battle, Darkness used his powers to enter into the Coliseum through cracks in the wall along with Takanuva. However, he was swept away outside the Hall of Masks after Tuyet unleashed her Water powers; it's currently unknown if he's still alive or not.

Powers and abilities
He had four clawed arms and could slip through the slightest spaces, but even The Shadowed One suspected that those were not his only powers. It seemed that one of these hidden powers was the ability to create stone barriers out of thin air.

Trivia

 * Darkness has found out that the Shadowed One found the virus on Xia, but he doesn't care. So long as the Shadowed One leads the Dark Hunters without showing any weakness, Darkness will not tell anyone or do anything about it.
 * Darkness does not wear the Kanohi Kraahkan in the story. He is depicted wearing it because that is how his maker chose to design him.