Kali linux uses the root user, since root privileges are needed to run various security tools like nmap and wireshark etc. However its uneasy to type the root/toor combination everytime Kali boots. So to make things simple just make the user root login automatically at system start.
And here are the simple steps to do it. Open and edit the file called /etc/gdm3/daemon.conf.
root@kali:~# leafpad /etc/gdm3/daemon.conf
In the daemon section uncomment the 2 lines for automatic login. It should finally look like this
[daemon] # Enabling automatic login AutomaticLoginEnable = true AutomaticLogin = root
Done. Now reboot and enjoy. You dont need to type the username/password again and again.