individual investorsthe federal governmentcorporate entitiesfinancial institutions
Individual investors don't regulate the market. If anything, a free market is good for them.
Corporate entities might be interested in the regulation of the market and many times they lobby to do so, but they don't have the power.
Financial Institutions also have nothing to do with marketing regulation and even though they are very influential, they do not have the power to do it.
So the one who regulates the market is the Federal Government.