Bohrok Gahlok
The Bohrok are driven by one purpose, to cleanse Mata Nui, restoring it to its former state as a completely barren wasteland. The Bohrok are controlled by the Krana, an intelligent organism, which they cannot function without.
The Gahlok are the trickiest Bohrok opponents – they never attack the same way twice! Able to control water, the Gahlok use tidal waves to flood Mata Nui. Remove their krana and they can be tamed.
After the defeat and imprisonment of the Bahrag, the Bohrok had their krana removed and were reprogrammed by the Matoran, to aid in rebuilding the Matoran villages.