Azalgors are fearsome semi-mechanical, semi-crystal beings that operate as a hivemind. Undoubtedly made by the Great Beings, the question remains as to WHY? The current theory is that they must have been another mistake, like the Zyglak were - until it was found that they didn't just drain elemental energy from artefacts and beings, but they could 'charge' things up with such energy as well.
However, Azalgors were still more dangerous than they were useful. They were attracted to Toa, and were a powerful danger to them as a toa's mask, weapons and attacks would simply be drained away. When disturbed, an entire hive of these creatures could fuse together into one giant Leviathan, which left to its own devices could disrupt the entire Weave!