Bitcoin is, in essence, decentralized. This means that there is no central control body within the network. Bitcoin is therefore not controlled by any entity, person or group of people. It is controlled by all members of the network: users, minors, developers.
Bitcoin: a decentralized autonomous organization
The governance of Bitcoin is therefore headless. It is often referred to as a decentralized autonomous organization (DAO) to describe it. Thus, each modification of the source code (defining the rules of the protocol) must be accepted and validated by all the actors of the network. Anyone can submit a source code improvement proposal – these are called Bitcoin Rush Improvment Proposals or BIPs .
Modifying Bitcoin therefore requires a consensus between all the nodes of the network. If anyone can use Bitcoin and come up with improvements, their proposal will be closely studied by all of their peers. This makes the decision-making process quite slow , but this type of governance brings great security to the system.
So, is it true to say that no one controls Bitcoin ? That no one can influence the decisions made for the development of the protocol? Obviously, this is an ideal.
Who changes the protocol?
Some voices carry more weight than others. For example, reputable cryptographers are given more consideration than a simple amateur coder . The team of developers involved in keeping the Bitcoin Core client software up to date, of course, has influence. Large miners also have very important voting power.
If an actor with much of the hashing power of the network objects to an update, they can easily block the decision making. This was the case during the implementation of Segwit in 2017. The disagreement over this modification resulted in the split of the blockchain, and the birth of Bitcoin Cash.
But, to conclude, the ultimate decision-making power rests with the users owning a complete node , that is to say a copy of the blockchain. These are the ones who disseminate and validate the transactions. Thus, they are free to install the version they want of the Bitcoin protocol, via their client software. They can thus accept or reject the modifications made to the protocol.