1: He is a supernatural being who seems to be of male-human form.
2: He is the source of all supernatural forces in the world of Dishonored.
3: He is able to grant powers to those he wishes.
4: He is neither good nor evil.
Did I leave anything out?
The Darkness, The Beyonder, Nocturnal, and many other characters like them came to mind when I first heard about The Outsider. I have to ask how much they have in common.
1: Are there more like him who simply haven't visited the world of Dishonored yet?
2: How long has he been interacting with the world?
3: Is he more a mindless force of nature, or does he have his own motivations?
4: Can his artifacts (such as the mask) be used the same way by someone other than who he gave them to?