Marvel President for Production Kevin Feige is a very informative interviewee, but he always says just enough. He is the president after all and no one can place a gag order.

He reveals the extent of James Spader's role as Ultron. He is not just a voice talent, they chose him for a complete performance. In an interview with the Huffington Post:

"Well, I think it will be more than a voice role -- we'll be capturing his face and his body to create a whole performance. He's a very unique and incredibly exciting and unpredictable actor. And Ultron in the comics is a robot, but what's cool about him in the comics -- and certainly how Joss Whedon is interpreting him for the movie -- is that he is much more than just a robot. That he's infused with much character. And I don't want to say too much, but you can imagine James Spader will be very dynamic in his portrayal of this character."

He reiterates: "We did not hire James Spader to do a robot voice."

The story will be a different from the comics. First of all, he was created by Henry Pym, a.k.a. Ant Man. Since Ant Man is yet to be introduced (his film is out two months after Avengers 2 AOU), they needed to make a variation. The hints point to Tony Stark/Iron Man.

The other difference is Ultron's motivation. One reason why Ultron is a recurring villain is his deep grudge on his creator, Henry Pym. Part of his anger is that he fell in love with Pym's flame, Janet Van Dyne a.k.a. The Wasp. How will they explore that angle? Will Ultron pursue Pepper Potts? If not, what would be his grudge?

Meanwhile, James Spader, in an interview from The Independent, talks on the Ultron role:"I'm not a planner. I like to try something different, to just see what happens... I think it'll be a lot of fun and it's incredibly nostalgic for me. When I was a kid my best friend had trunks of comics and I didn't have any so I used to love going for sleepovers at his house. Also I have three sons and two of them have a great interest in comics so they're excited I'm playing the role."