Andy Serkis thought he had a three-week voice-over stint.

But the actor's pivotal part as Gollum in The Lord of the Rings trilogy ballooned into four years of grueling labor in confining skintight suits that isn't over yet.

Gollum, the hobbit-turned-tortured-creature after being corrupted by the evil ring that Frodo the hero hobbit (Elijah Wood) now carries, briefly slithered on screen in last year's The Fellowship of the Ring. But in The Two Towers, which opens today, he crawls out of the dark and into a major subplot as guide to Frodo and Sam (Sean Astin).

Serkis, 38, a British character actor (Mike Leigh's Topsy-Turvy), says he often approaches roles physically. After Rings master Peter Jackson saw tapes of his recording sessions in which he acted out Gollum's reptilian crawls, the director decided to use motion-capture technology to trap that performance on film. In other words, an emoting human lurks under the digital skin and bones.

Says Serkis: ''He wanted Gollum to be the most fully integrated digital character ever, actor-led as opposed to being led by animation with a voice dropped in.'' Yes, he's far-far from Jar Jar.