If you want to get the fullname and not the user id, you can get from /etc/passwd and get your line with grep; or simpler with id -P which get the line for the current user; and, in all case, something like that:

id -P|cut -d":" -f5,5|cut -d"," -f1,1

(first cut to get the GECOS part, then 2nd cut to get the fullname, in case other info is present)