Well I think there is a way taking it back if your user have sudo prvilage and you find out that username?
well let go through it...
first you must find a live OS. you can use Kali in live mode , Ubuntu in live mode or whatever.
mount the hard disk that has Kali or the root of your Kali OS.
find /etc/passwd and open it... you might find the username you set inside it. something like this:
user:x:1000:1000:USER,,,:/home/user:/bin/bash
that's your username.
Hopefuly you know that username pass else you are screwed. if you have the pass you can login to kali with your own username.
to change root. you must use this command:
sudo su -
prompts your username's password.
now you have access to root!!!
change your root pass by passwd
Not sure if Kali is different from any other default setup (thus only a comment), but I'd assume mount the partition containing
/etc/passwd
and change it? – None – 2015-12-05T15:42:02.4501Which Kali Linux version you are running? – None – 2015-12-05T15:58:08.113