User blog comment:Stormwell/Timeline of Events/@comment-24029008-20140602202300/@comment-24029008-20140602213950

also, extending TheSweeper's thought, it makes a lot of sense that The Outsider is a name that the Abbey came up with to have something to call the Void entity, yet The Outsider introduced itself by that very title to Corvo, so I guess he just said why not, and adopted the name.

Either that, or The Void spawned him with a nametag :)