The Bitcoin Core project has a large open source developer community with many casual contributors to the codebase.
There are many more who contribute research, peer review, testing, documentation, and translation.
Project maintainers have commit access and are responsible for merging patches from contributors. They perform a janitorial role merging patches that the team agrees should be merged. They also act as a final check to ensure that patches are safe and in line with the project goals. The maintainers’ role is by agreement of project contributors.
Everyone is free to propose code changes and to test, review and comment on open Pull Requests.
Anyone who contributes code, review, test, translation or documentation to the Bitcoin Core project is considered a contributor.
The release notes for each Bitcoin Core software release contain a credits section to recognize all those who have contributed to the project over the previous release cycle.
A list of code contributors for the last year can be found on Github.