If you're heading out to watch The Hobbit: The Battle of the Five Armies, odds are that you have at least a passing familiarity with the complex mythology underpinning J.R.R. Tolkien's Middle-earth saga. If you don't ... oh, boy, do you have some catching up to do. And fast.
Luckily, CGP Grey has put together a four-minute (or so) primer, with nifty illustrations, that may help. Of course, it may also leave you tearing at your hair and shouting, "Wait, who's Eru Iluvatar again?" and "But where the hell did Hobbits come from?" (It serves you right for coming in at the end.) But, hey, that's preferable to trying to slog through the The Silmarillion.