And who controls the corporations? Shareholder activism is really limited; to a great extent execs can pay themselves what they want, hire who they want, and donate to the politicians they want.
But that's a completely different dynamic. It's like saying "who controls the government" because democratic control is really limited in a two party system where both parties have similar (or equally problematic) policies on many issues, unelected administrative agencies have wide latitude to set policy (including ones that profit them personally through the revolving door), government employees and government employee unions are a large voting and lobbying block despite the obvious conflict of interest against other citizens, etc.
The problem isn't that Bill Gates has too much money, it's that we have institutions with too much power and not enough accountability, both government and corporate. And then they use that power to conspire together against ordinary people.
What we need is to shrink the size of all entities to be less monolithic and more local and manageable.