Henry Darger is the ultimate example of outsider art. He lived and died as a custodian in Chicago, and upon his death when they cleared his room, people found a 15,000+ page manuscript and some several hundred illustrations. Never making art for anyone but himself while in his own little world after work, these illustrations really show some innocence and magic.
Check out the documentary, recently winning the Toronto Independent Film Festival, In the Realms of the Unreal. http://www.imdb.com/title/tt0390123/