Directed and produced by Peter Jackson and co-written by Jackson, Fran Walsh and Philippa Boynes, the fantasy film is the second chapter in the three-part trilogy based on J.R.R. Tolkien's fantasy novel, "The Hobbit."
Cumberbatch not only lent his distinctive voice to the gargantuan, treasure-hoarding villain Smaug at the center of the piece, but he also allowed his physical movements to be digitally recreated as the animated character through motion-capture technology.
The 37-year-old actor said he traveled to New Zealand where the live-action scenes for the movies were shot so he could work directly with the filmmakers to make Smaug look and sound as fierce as possible.
"It was hugely, hugely helpful. I started off with Peter and Fran and Philippa -- just the three of them and me -- which was a privilege in itself because of how large everything else is on this film, so I had their sole attention," Cumberbatch told reporters in Los Angeles recently. "We were in the motion-caption stage, so it started as a physicalization. Voice and face and body work. The whole thing. So, that's how I kind of discovered him."
Cumberbatch said he first became aware of "The Hobbit" when he was 6 or 7 and his father read it to him.
"It was a bedtime treat at home, so that was my first bit of research and then I went to the reptile house at London Zoo and had a look there. It's so beautifully written in the book and it's so well illustrated in countless editions of the book and then with Peter's input and our rehearsals and playing like a kid really in this incredible freeing mo-cap stage, as they call it, meant we could go anywhere with it. It was very, very helpful."
Although Cumberbatch spent time with Jackson, he had very little interaction with his co-stars, such as Richard Armitage, Martin Freeman, Ian McKellen, Orlando Bloom and Evengeline Lilly, until they started promoting the film.
"Sadly, I hardly met any of the cast. Richard, I met once. I crossed over people as they came back to do their third stint," he recalled. "I didn't spend any live time with Martin, which was sad. But, no, it was fine. We know each other quite well. ... But I have scenes with people I haven't even met yet, which is bizarre."
So, how did Cumberbatch "act" like a mythical creature?
"It's, obviously, more abstract," he said of playing an animated dragon as opposed to a live-action human. "It's only going to be an impression of something that is a serpentine reptile, who can breathe fire and fly because I am a limited, bi-ped mammal. Sorry about that. But Peter knew that when I auditioned, so we worked with my negatives and tried to turn them into positives. But one of the ways I did it was by squeezing my legs together and just forgetting the fact they were legs and feeling that as an elongated body, crawling around on the floor on my elbows and using my hands as claws and sort of over-articulating my neck and shoulder to the delight of any physio who was unlucky enough to try to heal me afterwards. Yeah, just throwing myself at it with a kind of kid-like imagination under [the filmmakers'] brilliant expert guidance. It was a really fun way to work."
Cumberbatch said he talked about the experience at length with "Smaug" assistant director Andy Serkis, an actor who had previously given critically lauded motion-capture performances in "The Hobbit: An Unexpected Journey," Jackson's three "The Lord of the Rings" films, "King Kong" and "Rise of the Planet of the Apes."
"Andy came down to start on the second unit and I thought, 'Oh, God, I wish he'd been there [while I was recording.'] Because he is the don. He is the originator. He is the master of that art form. Give it its proper title. And we just sort of laughed about it after because he's only done biped mammals. No one's tried a serpent before.
"I don't think he would have been much help at all [if he had been there,]" Cumberbatch laughed.
While Smaug is seen trying to kill Freeman's hobbit character Bilbo in an epic battle scene in the film, Cumberbatch didn't collaborate in person with Freeman. Cumberbatch admitted that felt strange since they are such good friends in real life after co-starring together in the hit TV show "Sherlock."
Asked what their next joint project might be, Cumberbatch teased reporters with the reply, "'Romeo and Juliet.'
"We like our Shakespeare. You know Martin would look very pretty in a blonde wig. The weird thing about it is there's all this chemistry and it was very peculiar acting by proxy with him [on 'Smaug'] and there's no joke to come out of that," he said.
"It's not like I can say, 'It's like that on the set at 221B Baker Street.' It's very light and brilliant and he's a bit of an inspiration to be around. That was the biggest con of what was otherwise... I mean hearing all these stories of the live-action perils and the amount of work these people put in. I did my job in about eight days and I feel like I'm the cheat at the table. But Martin and I will probably have some kind of outing in the future. Who knows? Who knows?"
So, what it is it he likes so much about Freeman?
"He's very smart," Cumberbatch noted. "He's really good company. He's one of the funniest people I've every met. He's a craftsman. He works incredibly hard and creates authentic characters and moments in drama and he's an inspiration to work opposite. I have nothing but good things to say about Martin."
"The Hobbit: The Desolation of Smaug" is to open nationwide Friday. Cumberbatch can also be seen in the current releases "12 Years a Slave" and "The Fifth Estate," as well as the upcoming release, "August: Osage County."