When you setup a new Ubuntu or OS X installation a user is generally created for you. On OS X it is whatever username you pick. On Ubuntu (the server version) usually the
ubuntu user is created.
The way I understand it, there is also a root user, which you can access via something like
sudo su - root, and entering the password of the
ubuntu or the user you created, which is part of the administrators group. Once you switch to
root I think you can use the
passwd command and change root's password.
But what was
root's password before that? Does it exist? Is it a random string of numbers and letters? How does the system deal with that?