“I’m playing Smaug through motion-capture and voicing the Necromancer, which is a character in the Five Legions War or something which I’m meant to understand. He’s not actually in the original Hobbit. It’s something [Peter Jackson]’s taken from Lord Of The Rings that he wants to put in there.”
The Necromancer is, of course, Sauron – who takes up residence in Mirkwood and is driven out by Gandalf “off camera” during The Hobbit. Sauron did not show up at the Battle of the Five Armies, but Cumberbatch here is clearly indicating he will be present. The Blastr folks theorize,
By changing this important part, Peter Jackson will neatly combine the two story threads: the one that follows Bilbo and the dwarves in their perilous quest through the forest of Mirkwood and then against Smaug underneath the Lonely Mountain; and the one which will follow Gandalf and his own posse, thus fleshing out the original story in The Hobbit book, and providing some of the material Jackson needed to split the story into two films.
It will also (still according to Empire Magazine) give a stronger motivation for those pesky nasty globins (and Wargs) whose king’s been killed, and who are also hoping to get their dirty hands on the dragon’s treasure as well (ah, goblins, greed and gold. Such a winning combo). IF they are thus led by Sauron, it will explain their later behavior in Jackson’s The Lord of the Rings films.
This is the kind of change that I think is eminently justified given that the story is being told in film, not 1000 page tomes, and which of course drives Tolkien purists into white-hot rage. Another example was the bit of political tolerance that Faramir displays towards the fallen Southron:
The enemy? [indicates dead Southron] His sense of duty was no less than yours, I deem. I wonder what his name is… where he came from. And if he was really evil at heart. What lies or threats led him on this long march from home. If he would not rather have stayed there… in peace. War will make corpses of us all.
I think this line was actually Sam’s in the book, though I’m not entirely sure. At any rate, Jackson has a duty to make the narrative fit the screen and I applaud these changes because they demonstrate a deep respect for the source material, not a flagrant disregard.