For years, the Bohrok's names were spoken only in whispers on Mata Nui: Lehvak, whose acid mist could dissolve anything; Gahlok, who brought the flood tide; Tahnok, whose heat could melt rock; Kohrak, who could freeze lava; Pahrak, who could crumble mountains; and Nuhvok, who dwelled in underground tunnels. Krana were strange and powerful creatures who controlled the Bohrok.
According to Nokama, the ancient prophecies said that the Toa would face a great challenge as they approached the Bohrok nests. The Bohrok would have eyes everywhere, thanks to the Bohrok Va. However, the Toa would not fear these creatures, but would use their wisdom and power to ensure that they could not warn the swarm about their coming. They would brave any danger to save Mata Nui and even dare to journey into the heart of the swarm. Deep in the darkness, they would use the krana they had collected to unlock six mighty exo-skeletons to increase their power. The would use them to confront the Bohrok queens in a titanic struggle that would shake the island itself. The ancient prophecies said the Toa would prevail, combining their powers to create a cell from which even the mightiest of Bohrok could not escape. After that, the prophecies were silent, except for a few haunting words that warned that with the merging of their forces, and the unleashing of so great a power, there was no telling what it might do and what the Toa would have become once it was all over.
The people of Mata Nui (at least Turaga Vakama) knew the legends of the Bohrok for centuries, although they prayed they were only legends. It was said the Bohrok slept an eternal sleep, waiting to hatch. Once awakened, the swarms were unstoppable – a force so powerful that they could reduce mountains to rubble and turn rivers dry. They were assisted by Bohrok Va – smaller, quicker creatures that acted as scouts and couriers. Each Bohrok carried a krana within it. The krana looked like a mask. The krana gave its Bohrok purpose and power, but it was also its greatest weakness, as any Bohrok could be humbled if parted from its krana. The legends did not say whether the krana came from Makuta. There were different swarms of Bohrok.