Yeah, it’s called Subsurface and we actually got an Oscar for that technology. That was something that had never been done before.

I remember reading that the reflection of light on and under Gollum’s skin and the way you could see his veins was one of the biggest innovations that you guys pioneered. Because he was so skinny, you saw all of the muscles moving under his skin. And because we were inventing technology as we were doing it, it was a huge challenge. Up to that point, you’d seen a lot of CG creatures, but none to the level of Gollum, where the detail him an actor on screen, rather than just a scary monster, which is what a lot of the CG creatures up to that point had been. His precious is the only motivation Gollum has left, once he’s left Sméagol behind, and it ultimately makes every decision for him - all the way up to his death.Eric Saindon: When we did Gollum, no one had really done a CG creature mixed with live action that you were supposed to believe was just a creature in the scene. He has but one goal, and that goal drives every single action Gollum undertakes. He goes by Gollum, and separated himself from any semblance of “human” desire a long time ago. That creature has his own name, separate from Sméagol’s innocent roots, and his own malicious personality. With that power, it warped him into the creature that we know from The Hobbit and The Lord of the Rings. Wracked by guilt and turned aside from any form of civilized safety, Gollum made a wretched life for himself away from any kind of human - or Elf, or Hobbit, or otherwise - connection, and this isolation gave the One Ring complete power over him. The One Ring’s corruption of Sméagol’s mind is entirely behind his transformation, as is that first violent act it compelled him to commit. The trinket’s attempts to return to its master failed, for decades, due to Sméagol’s seclusion, as he slowly transformed from a carefree Stoor into the hacking, miserable Gollum. So he retreated, far from his own kind, into the darkness that beckoned him more and more the longer he held the corrupting One Ring. Murder isn’t accepted much of anywhere, and it turns out even Hobbits are pretty strict in their upholding of those “no murder” policies, which left the warped Sméagol with nowhere to go. After stumbling across the One Ring and subsequently murdering his best friend for it, Sméagol was exiled from his home. Sméagol’s transformation from a youthful, naive Stoor to the twisted, broken wreck he becomes started long before the story in The Lord of the Rings begins.

Gollum in lord of the ring origin