Surely Andy Serkins has to have seen this film,
The voice likeness is just uncanny!
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"Never finish what you can't start!" ;)
Actually, Serkis based Gollum's voice off of Peter Woodthorpe portrayal as Gollum in both the animated version and the radio adaptation of 'The Lord of The Rings'. Woodthorpe may have based it off of Tolkien's own reading of Gollum's dialogue or the fact that Gollum is just written that way... as is Gurgi.
Formerly KingAngantyr
I don't think Andy Serkis's Gollum voice is anything like Peter Woodthorpe's. Only that, obviously, sometimes they were saying the same lines! Both are brilliant interpretations of Gollum in their own right.
Whether it's a coincidence that Gurgi sounds a heck of a lot like Andy's Gollum... The voices are very similar! In fact, no-one could watch The Black Cauldron and not think of Gollum (unless they'd never seen LOTR).