No. 44 The Mysterious Stranger is a book written by Mark Twain near the end of his life. In fact, it was not published before his death, and it was left up to his friends and the organizers of his estate to comb through his leftover maniscripts. Thing is, they didn't really like this one. It was pessemistic and confusing, plus heavily critisized Christianity, going as far as to say the whole idea was rediculous and that God didn't exist. So they took some of the plot form an earlier, unfinished draft, changed some charcaters, slapped on the ending of the most finished draft, and called it a day and hoped no one would notice. This version is known as just The Mysterious Stranger (minus the "No. 44" at the beginning). Wikipedia dubbs this the "Paine-Duneka text of 1916" and while it is in public domain, making it the most accessbile version of the story, it's estimated that only a quarter of it can be considered Twain's original work.
The original manuscripts were later discovered with the newer names of the characters crossed out and replaced with the old ones, written in Paine's handwritting.
It's very easy to tell the difference, the first (fraud) eddition stars a teen boy named Theodor who, along with his two friends, is visited by a mysterious teen boy who calls himself Satan or Phillip Traum. In the real version - called "The Printshop Version" - a teen boy named August is visited by a mysterious teen boy who calls himself No. 44. The stranger here plays a similar role, though Satan is far more meanspirited and 44 just seems completely unaware, and as mentioned above, they both end with the exact same chapter.
The book has three major movie adaptations. The first was a made for TV movie released in 1982. It's based on the real book (even featuring a text scroll at the beginning telling you this history of the fraud case, someone here is speaking my language) and is about as cheesy as any Medieval period piece based on an obscure book can be. It's delightfully charming. The second is a short scene from one of the earlier drafts, The Chronicle of Young Satan, which was adapted into a scene in the claymation film The Adventures of Mark Twain. This scene, and therefore this movie, is known for being pretty disturbing, and a clip on YouTube claims it is the " creepiest scene in a kids movie" (one of those facts is arguable, the other is blatantly false). The last full adaptation is one I have not and possibly will not ever get to see, a 1998 Soviet film directed by Igor Maslennikov titled Filipp Traum, which is almost impossible to find these days.
There have also been a handful of small theater productions and short film projects - after all, the fraud version of the book is in public domain.
