James Spader is doing an ''unbelievable job'' as Ultron, says Kevin Feige.

The 54-year-old actor has been cast as the titular villain - a crazed robot who develops a god complex and wants to destroy all of humanity with his incredible powers - in 'Avengers: Age of Ultron', directed by Joss Whedon.

Marvel Studios boss Feige is thrilled with Spader's work and claims the character has got an ''extreme personality'' in the forthcoming film.

He told Movies.com: ''Also our bad guy is great. I think people are going to be very, very excited to see what we're doing with the voice that Joss is bringing to life with James Spader for Ultron.

''We love Ultron from the comics, and have always loved Ultron, and at no point do we want him to just be a robot. We want him to have an extreme personality and attitude, and James Spader is doing an unbelievable job.''

Feige is hoping to keep fans on the edge of their seats while they watch 'Avengers: Age of Ultron', which is due for a 2015 release.

He added: ''Again, for us it's always about subverting expectations. Whenever you think you know what's coming next, we surprise people or deliver it in a slightly unexpected way. And Spader is doing that with Mr. Ultron.''