Because every large galaxy appears to have a massive black hole in its nucleus, we believe that the black holes play a critical role in galaxy formation -- but we don't know if they are seeds around which galaxies formed, or if they reflect the processes during formation that led to matter collecting in them, or whether both ideas are partially correct. In addition, the physical environment in AGNs is far more extreme than anything we can produce on Earth, and studying them is interesting because of their strange behavior but also to probe our understanding of physics.