James Spader says new 'Avengers' villain Ultron has a ''strange sense of humour''.

The Emmy Award-winning actor was personally asked to join the cast of 2015's 'The Avengers: Age of Ultron' as the titular villain and reveals that director Joss Whedon felt he was perfect to bring the unique character to life.

He said: ''A couple of years back I met with [Marvel Studios president] Kevin Feige at Marvel and told him it'd be fun to do something in one of his pictures and he agreed, but said they had to wait for the right thing. Then a month ago, he called me and said, 'We've found the right thing.'

''Joss Whedon called me and said, 'I really want you to do this.' He said this character had a strange sense of humour and some painful issues but he was able to retain a certain gravitas despite this. So I suppose I'll be making a fool of myself while still retaining a certain gravitas. I'll do my best to pull that off.''

Spader admits he wasn't aware of Ultron in the Marvel comic books but is aware that it's important to pick the right part to play in comic book films because they have such rabid fan bases.

He added to ShortList magazine: ''Your choice of character is very important in that world ... you're stuck with it forever.''

'The Avengers: Age of Ultron' is due for release in May 2015.