When you want to say "this..." You say αυτός ο.../αυτή η..../αυτό το... . "That... " is "εκείνος ο.../εκείνη η.../εκείνο το..." For example: this day=αυτή η μέρα, that thing=Εκείνο το πράμα. Αυτός/αυτή/αυτό means he/she/it but in Greek (which is a null subject language) actually using it results in "this..." F.e: this is the right choice=Αυτή είναι η σωστή επιλογή. It is the right choice=Είναι η σωστή επιλογή. In questions, where the object is required (Greek does not have the ability to drop the object too!) phrases like who is he/who is this are translated ποιός είναι αυτός, because as you noted αυτός is also he.
Okay, so as long as the verb agrees then the context should bear out who/what you are speaking of.
Still one question: Why is there a definite article in this sentence: "Αυτός ο λύκος δεν τρώει ψωμί"
Can this sentence be said this way: "Αυτός λύκος δεν τρώει ψομί"
Thank you for your answer.
Αυτός ο λύκος means THIS wolf (and not any other wolf) And αυτός could never mean "it"; "it" would have been "αυτό". "he" on the other hand could be translated as "αυτός" (i.e. "he writes" = "αυτός γράφει", however, in Greek, like in Spanish, we don't use the pronouns to designate the subject of the verbs; the subject is inferred by the verb's conjugation.