From the AIX login command manual:

The login command also sets the LOGIN and LOGNAME environment variables.


sudoers(5) does not mention the LOGIN environment variable.


From the AIX su command manual, the hyphen flag:

Specifies that the process environment is to be set as if the user had logged in to the system using the login command. Nothing in the current environment is propagated to the new shell.


Example:

$ su - -c env | sort > su.env
root's Password:
$ sudo -i env | sort > sudo.env
$ comm -23 su.env sudo.env
AUTHSTATE=compat
LOGIN=root
$ comm -13 su.env sudo.env | grep -v '^SUDO_'
USERNAME=root
$ uname
AIX
$ oslevel -s
7200-02-02-1832
$ sudo lssec -f /etc/security/login.cfg -s usw -a auth_type
usw auth_type=STD_AUTH
$ find /usr/*bin -inum $(ls -i /usr/sbin/login | awk '{print $1}')
/usr/sbin/getty
/usr/sbin/login
/usr/sbin/tsm
$