2. The Necromancer
This one is also sort of cheating, because as any die-hard Tolkien fan can tell you, the Necromancer is actually the painstakingly-rebuilt spirit of Sauron, the Lord of the Rings himself. However, this is another artifact of Tolkien's late-in-the-game decision to re-jigger
The Hobbit to fit with the bigger history he'd created with Middle-earth (he also went so far as to release a later version of
The Hobbit with some minor-but-critical changes to the Riddle Contest). The thing about the Necromancer is that we have a character who is almost totally open to interpretation. We caught a glimpse of Sauron's physical form in the prologue scenes of
The Fellowship of the Ring, but hopefully Jackson and company will take the chance to give us something new with the character. The Necromancer isn't given much description, and it's not even made clear what sort of form (physical or otherwise) he takes during his time spent in the stronghold of Dol Guldur south of Mirkwood. Of course, we know that we'll at least hear him because someone has been cast to provide his voice. The same actor, in fact, who is responsible for our final and most-anticipated character.