There is a special user called root on Unix systems which has all the privileges which can give permission to any user on any file.
Some users who are allowed to act on behalf of root are called sudoers. This list of sudoers can be edited using sudoedit command. Such users are allowed to run commands as if they are root using: sudo
You can change the owner of a file using chown and change the group of a file using chgrp command. Please note that changing the owner of the file is possible only with administrative account.