Who develops the Bitcoin Cash protocol?

The Bitcoin Cash protocol is not controlled by any single individual, institution, or development team. Anyone is free to contribute. A lot of the work is done as a collaboration between the various full node development teams and other independent developers.

While not an official collaboration website (with Bitcoin Cash there is no such thing as “official"), much of the collaboration on protocol and consensus work is done on bitcoincashresearch.org. Anyone can sign up and contribute to the discussions taking place there.