Sharlto Copley was a producer, writer and director of short films—including director Neill Blomkamp's Alive in Joburg, the basis for Blomkamp's feature-film directorial debut District 9—but he makes a big impression in the lead role of Wilkus ver der Merwe in District 9, his first acting role.

"Normally I would be behind the scenes, and it's just so stress-free, relatively speaking, as an actor," Copley said in a new conference over the weekend at Comic-Con in San Diego. "Because you know it's improvised, you go there, you show up, it's like, 'Dude, you got to go there, find the weapons, this happens, go,' and you are either the character or you're not. You don't have the stress of 'Is it working? Isn't it working?' That was Neill and [producer] Peter [Jackson]'s problem. I just got to play around in the dirt, which wasn't as fun, but you know." (Spoilers ahead!)

In the sci-fi action drama, Wilkus is an agent of Multi-National United who gets exposed to an alien fluid with unexpected results. The only place for him to go is the segregated alien township, where he forges an uneasy alliance with an alien.

"It was a very natural process," Copley continued. "I mean, I'm not an actor, but I've done a lot of characterization stuff in my life. Like, when I was a kid, I used to make stuff and do characters and voices. So improvisation and caricatures and character and that sort of thing was always something that I felt very comfortable with. Making the film and working with Neill as we did in the process of shots, by the time I was actually there with the full form, it was the cool team of people I've sort of worked with before on previous stuff, so I was very relaxed, and [it was] awesome."

Perhaps that's because Blomkamp created an environment that was less about acting than actually playing as if it were reality. "There was a lot about the film that felt like Neill was coming up with ways to see if I would do it, because I was always determined if I was going to act, that I was going to be an actor who just did everything," Copley said. "So it was constant testing. That's how it felt. Like, put the sandwich in the real garbage. There's human feces around. He's got to [root] through the garbage, get the real trash on his hands, and he's got to eat the sandwich."

The biggest stretch for Copley was playing a lefty. Blomkamp tricked his right-handed friend into establishing Wilkus as sinister (in the Latin sense of the word). "That was Neill only telling me after I'd committed in continuity to hold the gun the wrong way," Copley said. "I knew it was going to look really uncool, because I was trying to sort of make him maybe a little cooler, Neill was like, 'No, no, no, it has to be that your trigger finger is the left hand.' So I got better. I got better with my left, I would have to say."

District 9 opens Aug. 14.