The Peter Jackson-produced South African sci-fi action hit District 9 might have no stars but its unknown lead Sharlto Copley is now on his way to becoming one. He talks to Russell Baillie

There are two sounds to be heard as Sharlto Copley talks. There's his Afrikaans accent which those who have already flocked to District 9 - it had a bigger-than-expected US$37 million opening weekend stateside - will recognise as the voice of the film's unlikely hero Wikus Van De Merwe.

But underlying his conversation is the sound of a guy still pinching himself in disbelief that he's at the centre of a film which has turned into a phenomenon.

"I am just trying to flow with that process rather than say I am going to be the next great thing. I could never have designed this situation, so clearly life has some kind of plan for me. Whatever it is I'm going along."

Copley has been involved in films and television in South Africa for most of his adult life, as a producer and director rather than an actor.

He gave District 9's then-teenage director Neill Blomkamp his first job in his visual effects house. He also produced Alive in Joburg, the spectacular short directed by Blomkamp about insectoid ETs taking up residence in Johannesburg shantytowns that became the working drawing for District 9.

That was after Blomkamp's supposed first feature - the Peter Jackson-produced film of the videogame Halo - fell apart and Jackson's partner Fran Walsh suggested Alive in Joburg as a template for a full-length movie.

With the project up and running, Copley thought he might have some backroom role in the production.

Instead he became the lead actor.

While still working on the script, Blomkamp had asked Copley to put together a shoot and play a bureaucrat dealing with the aliens in a promo piece to show Jackson and the film's backers. It turned out to be the audition he didn't know he was having.

"I literally just found a voice for the character and let him come out in the test I shot for Neill without knowing in any way that I was testing for the film.

"We just thought we were exploring something for something he was writing and he'll get a proper actor later."

Blomkamp was hooked and seeing the footage, Jackson signed off on the unknown Van der Merwe.

"We were dubious about him at first," Jackson told Empire, "But he's the key to the improvisation working. He's got what Ricky Gervais and Sacha Baron Cohen have got - he's fearless, naturally very funny and also touching."

Suddenly Copley found himself the man in Blomkamp's fast moving frame. And quite aside from being the lead character, this was in a film where all the dialogue was to be improvised and much of the alien presence was going to be added after the cameras stopped rolling.

Copley says his own film background helped in the shoot in the Soweto squatter camp area of Chiawelo.

"Yeah, in a sense that I was a new actor but I wasn't new to film-making. The way that Neill worked - allowing me to improvise all my dialogue, allowing me to turn all the scenes on their head if something cool came out - the fact that I was aware of continuity, camera angles, visual effects issues, made it easier for the crew."

We first meet Van De Merwe in his role as a loyal employee of the MNU corporation, a firm charged with looking after the apparent refugees from outer space.

They have parked themselves on the Johannesburg skyline and then been forced into internment in the area of the title.

Wikus is moustached, insecure, trying to impress and not particularly likeable. Copley laughs loudly at whether other than the growing the mo, the character was a stretch for him.

"I was just trying to play that guy as somebody you could laugh at but hopefully not totally dislike. You would laugh at him."

For the latter stages of the film, once Wikus is on the run from his employers and appears to be mutating after exposing himself to an alien concoction, Copley had to spend the first six hours of his working day in a makeup chair getting prosthetics and makeup applied by the Weta Workshop team.

"It was pretty gruelling but it was so helpful to inform the character. I didn't know what that character was going to be in two thirds of the movie when his transformation starts. That was when Peter and Neill were taking a chance - they had seen me as the bureaucratic guy in the beginning but they hadn't seen any dramatic stuff from me at all and I had never done anything remotely like that.

"So the prosthetics really helped me bring that out. The day I got that stuff on I thought 'this is really going to be a problem for the man, it's really going to be mixing him up. His old life is being stripped away."'

So is Copley's. He first realised his life might never be the same after finally seeing the finished film at San Diego's Comic-Con convention where he and Blomkamp were guests of honour.

"Suddenly it all got very real at that moment. Before then we were just having fun and Neill was just letting me play around and there were a lot of friends working on the film. And all of a sudden the pressure of 'Dear God, I hope they understand the accent'."

It appears they do. But also, how District 9 comments on South Africa's apartheid past, and still-troubled present, gives the film a depth below the action and the gore.

How that will play at home he doesn't know.

"I hope people will be inspired to see an Afrikaans character played with a redemptive quality. Afrikaaners have just held this guilt for apartheid - fair enough in some instances but it's also remarkable what they actually did in the end, giving over the power that they had."

"They're just the bad guys every time and people are getting annoyed with the fact that it is always some kind of apartheid movie, some kind of heavy thing. But [District 9] is lighter in effect but deeper if you want to go there - but you don't have to."

For himself, Copley is now sold on acting. Yes, he would happily sign up for a sequel. But he's got his eye on opportunities further afield. So he wouldn't swap with his old mate Blomkamp?

"No. I've directed a movie before and I probably will again but acting is just so much more fun. I have never heard a director say 'it's been an absolute breeze of a time'. If they do, they are probably lying."

Who: Sharlto Copley, the star of the acclaimed low-budget sci-fi thriller District 9
When and where: At cinemas now