oracle dba account - connect through

The system user has the dba role granted. On most systems this user is regarded as an internal oracle admin user not used by administrators unless you have to. Administrators should have their own named users with all the necessary rights granted.

If you for some reason want to lend someone an admin user without giving them the password you can use this trick. Shown with user system, but it works for any user.

SQL> create user kpe identified by kpe;
User created.
SQL> alter user system grant connect through kpe;
User altered.
SQL> connect kpe[system]/kpe
Connected.
SQL> show user
USER is "SYSTEM"
SQL> alter user system revoke connect through kpe;
SQL> drop user kpe;