- You still don't know who (which individual) is behind the BTC address, because bitcoin is anonymous.
- It is decentralized, but some exchanges process big percentages of conversions. Transferring the coins to other BTC wallets is decentralized. Moving it out of the BTC blockchain is often done through exchanges though, but there's a lot of them, and you can avoid the exchanges as well.
- No, everybody controls it; it's a consensus-based system, so if enough people agree on taking things in one or another direction it will. Look up "hard fork" in the context of BTC.