The Lehvak were the swamp Bohrok, one of the six breeds of Bohrok swarm. Their head-plates housed red Krana, which were telepathically directed by the Bahrag.

History

The Great Beings created the Bohrok machines 100,000 years ago, placing them under the guidance of the Bahrag queens. The Bohrok's purpose was to scour clean the outer surface of the earthen dome housing Metru Nui and its silver sea, which protruded out of the ocean of water on the planet surface like a large island, should anything have settled on it. This was supposed to ensure the well-being of the Great Spirit, Mata Nui, in some way. The Lehvak, along with the five other Bohrok breeds and the six Bohrok Va breeds, were stored away in chambers combed with individual containers located beneath both the outer surface of Metru Nui's dome as well as below Metru Nui itself. The Bohrok were put fast into hibernation to awaken only when they received a sonic signal when the time came for them to perform their task.

No inhabitants of the universe were ever intended to live on the surface island. Because of circumstances surrounding the Great Cataclysm 1,000 years ago, however, the Matoran of Metru Nui were forced to emigrate to the island. The Cataclysm had also caused a massive conduit of energized protodermis beneath the island to rupture and wash over all its terrain. The substance caused massive transformations in the landscape, bringing forth plantlife and sharp climate shifts where before there had only existed a rocky wasteland. The changes acclimated the environment nicely to suit a new home for the Matoran, who named the island "Mata Nui" in honor of the Great Spirit. Eventually myriad species of Rahi beasts settled on the island as well after the Matoran.

This disruption of Mata Nui's original state allowed the Makuta of Metru Nui to exploit the Bohrok's function. The Makuta of Metru Nui came to Mata Nui 999 years ago. Intent on perpetually harassing the Matoran and keeping them from ever returning to Metru Nui, less than one year he awakened the Bohrok prematurely in order to bide his time after his first defeat by the Toa Mata. The Lehvak and other Bohrok quickly emerged from their chambers in droves, rampaging across Mata Nui and devastating its lush landscape. To defend the Matoran and their home, the Toa Mata continually put up resistance against the Bohrok swarms. The Bohrok, however, never attacked the inhabitants of Mata Nui unless they directly obstructed their mission; they simply campaigned across the island intent on reverting it to its original barren state.

Many Bohrok, Lehvak among them, were incapacitated in the struggles against the Matoran. The Matoran realized they could dismantle fallen Bohrok and rebuild them into Boxor vehicles.

The Matoran considerd the Lehvak to be the most dangerous Bohrok type, since their acid spray was capable of rapidly dissolving any substance on Mata Nui. When the Lehvak invaded Le-Koro, Turaga Matau and the resident Le-Matoran put up resistance against them. The Lehvak slung their parasitic Krana onto their faces to enslave their minds to the swarm, ending their threat. Toa Lewa, when he came to investigate Le-Koro, also fell under their control. Toa Onua later rescued Lewa, and a group of Matoran with Boxor vehicles rescued Matau and the Matoran.

Lehvak also lay siege to Po-Koro to reinforce swarms of Tahnok and Pahrak. Their arrival heralded the evacuation of the village.

After a week of the Bohrok's rampages, the Toa Mata ventured down into the Bohrok nests to challenge their source of direction: the Bahrag twins. The Toa Mata successfully sealed the Bahrag away in indestructible protodermis with their elemental powers. The Bahrag's telepathic link to the Bohrok's Krana was severed, and all Bohrok stopped in their tracks.

After the Bohrok were defeated, the Matoran found out they could remove their Krana and give them new commands verbally. The Matoran put the Bohrok to work rebuilding the damage they caused to the villages.

The emergence of the Bohrok-Kal failsafes sent a signal that caused the Lehvak and other Bohrok to return to their nests automatically. The Toa, transformed into more powerful Toa Nuva, narrowly stopped the Bohrok-Kal from restarting the swarms; but the Bohrok swarms remained underground, dormant in their nests.

The later defeat of Makuta allowed the inhabitants of Mata Nui to move back to Metru Nui.

Recently the Toa Nuva returned with better knowledge of the Bohrok's relevance to the will of Mata Nui to the the Bahrag's lair in order to free them and restart the Bohrok swarms. With no Matoran living above to be threatened, the Bohrok awoke a second time, this time successfully wiping out the Matoran's old homes and reverting Mata Nui back to its original state, although they met resistance from the wandering Kardas Dragon from Voya Nui. The Kardas Dragon took out a number of Bohrok machines but was severely beaten down. When the Bohrok's task was done, they returned to their nests.