MariaDB Plc. appears to be the top contributor to MariaDB's codebase (81.9% of commits since the beginning of 2020)[0].
[0]: https://mariadb.org/mariadb-contribution-statistics-march-20...
[0]: https://mariadb.org/mariadb-contribution-statistics-march-20...
For context MariaDB existed before 2020, Before the Plc, since 2009, and will continue to exist after.