What would happen if Bill Gates invested all of his money in Bitcoin?

First, it would be extremely dumb of Gates to do this. Why? Because at any time, the community could realize this and fork the chain and take the utility of the blockchain with it to a different iteration of Bitcoin, leaving Gates with a worthless bunch of nothing.

If Gates’ (or any wealthy person’s) plan was to control Bitcoin, they’d use immense wealth to buy or rent computing power to launch 51% attacks against the chain.