Originally Posted by LoDam
As lugoteehalt said, Ubuntu has no root user (unless you added one)
That's incorrect, and not what lugoteehalt said. Ubuntu does have a root user. By default the root account is locked.
Assuming the OP has deleted his main account and logged off/rebooted then he can't put sudo in front of anything because he can't login.
You need to boot into recovery mode. Hold shift during boot if you're not presented with a list of OSs to choose from normally. Once you have a root shell you can add your user account again. Reboot once you've finished.