Ethereum is not controlled by any particular entity. Ethereum exists as long as computers running software that follows the Ethereum protocol, connecting to each other, and adding blocks to the Ethereum blockchain. Each of these computers is called a node. Anyone can run a node, but they must stake Ether (Ethereum's native token) to participate in the work of securing the network. Anyone can stake 32 Ether without permission.
Even Ethereum's source code is not generated by a single entity. Anyone can propose changes to the protocol and discuss upgrades. There are several implementations of the Ethereum protocol done by independent organizations in multiple programming languages, which are usually built on an open basis and encourage contributions from the community.
