Who controls the Bitcoin network?

No one owns the Bitcoin network, just like no one owns the technology behind email. Bitcoin is controlled by all Bitcoin users around the world. While developers improve the software, they cannot force changes to the Bitcoin protocol because all users are free to choose the software and version they use. 

In order to be compatible with each other, all users need to use software that follows the same rules. Bitcoin can only work properly if there is a complete consensus among all users. Therefore, all users and developers have a strong incentive to protect this consensus.