A new breed of actor is taking a star turn in Hollywood. They don\u2019t hide out in their trailers, check into rehab in the middle of a shoot or sleep with their costars. They do their own stunts, can shoot take upon take and don\u2019t require residuals. Digital actors. Synthespians. Virtual stars. Whatever you want to call them, these artificially rendered stand-ins are popping up in more movies, from a major character in the latest Lord of the Rings installment to the eponymous lead in next summer\u2019s The Hulk to various characters in The Matrix Reloaded due out in May. High-tech special effects houses are using ever-advancing computer generated imaging (CGI) artistry and motion-capture technology to take the movements and voices of real actors and create a digital depiction of their actions and expressions. Such techno-tricks have created virtual backdrops and minor background characters for some time; it\u2019s the human qualities portrayed on-screen that are getting better and leading to better roles.In theaters now, Lord of the Rings: The Two Towers showcases the character Gollum, a hobbit-like creature who is digitally transformed into something far more frightening because of his extended encounter with the ring. He\u2019ll be one of the the most lifelike synthespians seen on the big screen, according to director Peter Jackson. Using the voice and movements of real-life actor Andy Serkis, Weta Digital, the Wellington, New Zealand, effects house working on the Rings trilogy, created the virtual actor using fluid dynamics (the study of how liquids and gases move) and vast amounts of new modeling codes that allow for convincing joint movement and translucent, fleshlike skin. At Industrial Light & Magic, the technology once used to create aliens is being used to generate photo-realistic digital doubles to perform stunts when a human actor can\u2019t, says Cliff Plumer, CTO of San Rafael, Calif.-based ILM. The company that used digital actors in the fight scenes in Episode II: Attack of the Clones and explosions in Pearl Harbor now creates digital models of main characters in its movies.Even so, stars like Gwyneth Paltrow and Jim Carrey have little to fear. For one thing, close-ups can be tricky, even though ILM is applying tools it used with The Perfect Storm in trying to get there, Plumer says. And, adds Ilyanne Kichaven, spokeswoman for the Screen Actors Guild in Los Angeles, "There will always be a need to see real performers on the screen."And, of course, it takes more than acting -- virtual or real -- to make a winning film. Simone, starring Al Pacino as the creator of a digital blonde superstar (played by the very real Rachel Roberts), bombed at the box office in 2002. It\u2019s unlikely that a synthespian could have saved this film that critic Roger Ebert says was "too shallow a picture."