Advanced robotic enforcers of Metru Nui.
In the complicated network of Metru Nui, something must be done to maintain order, and keep the city running smoothly. That something is the Vahki. Created by the gifted engineer Nuparu at Turaga Dume’s request, these machines patrol the streets on the lookout for dangerous criminals. Thanks to the city’s lack of a native Toa team prior to the Mangai, they also served a secondary purpose of guarding Metru Nui from outside threats.
Being purely robotic beings, Vahki don't have much of what you'd call a 'personality'. Depending on the situation they can range wildly from comforting and protective to terrifying and ruthless. Fortunately, their orders come directly from Turaga Dume, so the Matoran of Metru Nui have nothing to fear.
Eight different models of Vahki were created. Six of these patrol each respective Metru, while the remaining two are elite models reserved for emergencies such as crowd control and rampaging Rahi. All six standard models of Vahki are equipped with both a Kanoka Disk launcher built into their head unit, and a pair of model-specific Stun Staffs to non-lethally dispatch their targets. While they can understand Matoran orders, Vahki can only communicate amongst each other via ultrasonic signals. Due to their limited emotional capacity, Vahki cannot be bribed or deceived, and thanks to their entirely mechanical form they can pursue targets to exhaustion. They are also quite intelligent, able to coordinate traps and ambushes. However, they can also be coldly single-minded in their duty. If they have been given orders to subdue a target, they will break down every door in their way to reach that target until ordered to stop.