While Lord of the Rings has bestowed instant fame on most of its stars, poor Andy Serkis (Topsy-Turvy, 24-Hour Party People) — the man behind computer-animated Gollum — probably won't be recognized for his digitized performance. As moviegoers will see in The Two Towers (opening Dec. 18), this creepy-crawly schizoid is certainly no shallow goofball like Jar-Jar Binks. Physically and emotionally speaking, Serkis says it's the hardest role he ever played.

"It wasn't just people acting to tennis balls on a stick," he explains. "We shot every single scene conventionally. I was in a skintight suit; I crawled around, physically moved as Gollum, doing the voice. That's why it works."

Indeed, the Rings animators based Gollum's every gesture and facial expression on Serkis's interpretation. Behind the scenes, they alternated between rotoscoping the character — that's the process of "painting" pixels directly over the actor's image — or using a second performance Serkis did in a motion-capture studio.

"It was physically very demanding," he sighs, "having to do every scene in two different manifestations. On set, it was hard enough, because you have rocks which you're crawling around on knocking your knees. I had to wear knee pads and elbow pads in the end. I did injure myself, and it put a lot of strain on my back. I could be 12-14 hours a day on all fours."

The resulting tragicomic character — who alternates between villainous temptations and glimmers of heroism — already has inspired some Oscar buzz. "There's been talk about it," he acknowledges. "Some people say maybe they should have a special category for being a digital thing. In my mind, it's no different from something like The Elephant Man, where John Hurt had 10 hours worth of prosthetics on his face."