Who runs dark pools?

Could you clarify who exactly operates these so-called "dark pools" in the world of finance? Are they primarily regulated exchanges, unregulated entities, or a mix of both? What kind of institutions or individuals typically have the means and motivation to establish and maintain such platforms? Additionally, what are the primary benefits and potential risks associated with dark pools for market participants? Lastly, how do regulators around the world view and attempt to oversee these opaque trading venues?