The database system administrator (SYSDBA user) is the first database user. This user is created when a database instance is created. The default name for the database system administrator is DBADMIN.
This database system administrator has the most comprehensive rights of all database users. The database system administrator is a database administrator who also has all the possible rights of a Database Manager operator (DBM operator).
Concepts of the Database System
Database Manager GUI, Managing the Database System Administrator
Database Manager CLI, Managing Database Manager Operators
Security Guide, Changing the Passwords of Standard Users