Original creators left and created MariaDB. MariaDB is now used in place of MySQL in most Linux distros by default. They left after Oracle got control over it by buying Sun (who had previously bought MySQL.)
The short version is that MySQL was acquired by Oracle (when Oracle purchased Sun Microsystems). Following concerns about it remaining open source, MySQL was forked by it original creator, and is developed as MariaDB[0].
Personally, I always though that the community over-reacted big time. After all, the core DB engine most people were using for MySQL for years (InnoDB) had been owned by Oracle for years before that.