[Leaf]

I am wondering why (apart from plot convenience) the Balrog showed up to hunt the fellowship down. We know that it didn't harm Gandalf or Aragorn on their earlier visits to Moria. We also know that Balin and his companions could live and labour in Moria for a few years without getting attacked by it, which is quiet odd if you think of the Balrog as a watchdog guarding his home. If I'm remembering correctly there isn't even a hint (e.g. in the book of Mazarbul) that the Balrog was involved in the final attack on the dwarves at all. Just drums in the deep. So the Balrog doesn't seem to be the most active fellow. At least not in the last decades or so. Was he, like all beings of evil, drawn by the ring? Was this the main reason he appeared?