root

Reference: http://www.cyberciti.biz/tips/recover-mysql-root-password.html (partly copied to avoid loosing source)

# /etc/init.d/mysql stop

Stopping MySQL database server: mysqld.
# mysqld_safe --skip-grant-tables &
[1] 5988
Starting mysqld daemon with databases from /var/lib/mysql
mysqld_safe[6025]: started
# mysql -u root
Welcome to the MySQL monitor.

A lot of people use the root account to do anything they need, just because it is easier… This is a really bad idea, as that user can do anything to the system.