From BS01:
The Bahrag were created by the Great Beings with the sole purpose of leading the Bohrok in cleansing the island of Mata Nui and crafting Krana for them.
The Bohrok Va were created by the Great Beings to assist the Bohrok in clearing Mata Nui, reverting it to its original status as a barren wasteland. Upon creation, the Va were placed in hibernation along with the other breeds of Bohrok, waiting for the time to be awakened to perform their duty.