Vahki

Vahki were robotic law-enforcers that kept the peace on Metru Nui.

Vahki of Metru Nui
The Vahki were commissioned to maintain law and order on Metru Nui. They were sometimes attacked and eaten by large Rahi nicknamed "Vahki Hunters".

On one occasion, Jarr destroyed three squads of Vahki using only his dagger.

At some point between 20,580-40,080 CMT, the Order of Mata Nui sent Kakamu to Metru Nui to disarm what was thought to be a bomb attached to a chute in Le-Metru, but was actually a Genetic Manipulator. The Genetic Manipulator deactivated once it had taken a genetic sample from Kakamu, so Kakamu assumed that the threat had been neutralized and handed the disarmed "bomb" over to the Vahki. The Vahki placed the Genetic Manipulator in a storage closet somewhere in the city, unaware that Kakamu's clone, Trantoshen, was growing inside it.

Malygos gained control of the Vahki when he became the new Turaga of Metru Nui. He sent Vahki to kill Jarr when Jarr threatened to destroy Xia unless he was given protosteel, but Jarr destroyed these Vahki and escaped.

The Vahki were presumably destroyed during the cataclysmic final days of the Matoran Universe.

Hapori Dume's Vahki
In 150,080 CMT, Hapori Dume summoned billions of Vahki through portals to attack the participants of the Battle of BZPower. The current status of these Vahki is unknown.

Alternate Universes
The Vahki were also used in the Dark Mirror Universe's version of Metru Nui after the fall of the Toa Empire. Helryx once threatened to unleash the Vahki on Ynot if he stepped out of line.