MariaDB is a community-developed, open-source relational database that began as a drop-in replacement fork of MySQL. The MariaDB Foundation’s own anniversary post records that, as Oracle moved to acquire MySQL, “a new upstart called MariaDB was born as a fork of MySQL,” birthed by MySQL founder Monty Widenius with the support of many of the original MySQL developers. The same post dates the first release, MariaDB 5.1.38, to 29 October 2009.
The fork was a direct response to ownership changes around MySQL. Because Oracle held the MySQL trademark, the new project needed a different name. The MariaDB documentation explains that Widenius kept his family naming tradition: MySQL was named after his first daughter, My, and “MariaDB continues this tradition by being named after his younger daughter, Maria.”
MariaDB was designed to stay compatible with MySQL so that existing applications could switch with little or no change, while remaining Free and Open Source Software under the GPL. Over time it added its own storage engines (such as Aria, originally called Maria) and features, and it became the default MySQL-compatible database shipped in many Linux distributions.