"Who is this?"
Does it literally mean who is he/ him and a different word for who is she and her?
You can ask "Хто це?" directly to an unknown person (over the phone, for example) or about a third person. While "Хто це такий?" can be only used about a third person. Plus the latter specifies gender (masculine), therefore you probably see who it is, but you want to know more details. The former is more a way to find out the identity of the person.