Get the initial username which you used to login to your Linux system

If you need the initial user which you used to login to your Linux system or the time when you login you can do:

whoami

One purpose of this could be the .bashrc to show different Bash Prompts for root to different users:

if [ $(whoami) = "root" ]; then
   PS1='${debian_chroot:+($debian_chroot)}\[\033[41;33m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
else
   PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
fi