Vahki

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

Vahki of Metru Nui
The Vahki were created in 96,080 CMT to maintain law and order on Metru Nui. Vahki were ocassionally hunted by a species of machinery-eating Rahi that gained the nickname "Vahki Hunters".

In 100,079 CMT, Malygos gained control of the Vahki when he became the new Turaga of Metru Nui. Malygos sent three squads of Vahki to kill Jarr when the Zyglak mercenary threatened to destroy Xia unless he was given protosteel, but Jarr destroyed these Vahki with his dagger and escaped.

The Vahki of Metru Nui were destroyed or decommissioned in the 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
Vahki were also used on 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.