The Vahki were designed by Nuparu to help keep the peace in Metru Nui, and were produced en masse by the city's Po-Matoran. It is believed that there were 5,000 Vahki created. With the ability to transform from a biped to a quadruped state, the Vahki were programmed with one directive: to preserve order and stop lawbreakers by any means necessary. Though Vahki often tried to stop the Toa Metru, they were not evil and obeyed any order they were given by Turaga Dume. They were well-known, and somewhat feared and resented, for being coldly efficient and dedicated. One thing that did deter them a bit was deep water - even the Bordakh model, which were better adapted for swimming than the other kinds of Vahki. Although capable of speaking the Matoran language, their speech was normally in inaudible frequencies, which were translated for Dume by special equipment. Despite not speaking at normal conversation speed, they appeared to be able to understand such speech. Each Vahki was also equipped with a built-in Kanoka Disk launcher and some flight ability.
When Makuta revealed that he had been posing as Dume for some time, he absorbed the city's entire power grid to increase his power quickly. Most of the Vahki that were in their hives were destroyed by the power surge, but the survivors changed... Their speech was now at normal speed and frequency, and their staffs could now destroy anything in their path. Most importantly, their programming was warped: they decided that order could best be kept in the city if nothing was left alive. However, even this new ruthlessness did not help them when the Visorak invaded the city and all of the Vahki were destroyed. Also, the Matoran will not create any new ones.
increbily, Emperor Fang brought the former enforcers to life, and created a new factory with millians of mindless worker driods to create more of the creatures. they are not considered to be dark spawn, cause of them being machinces.