[Raynor]

Originally Posted by davem

We have here not so much a 'split personality' as an individual who makes a moral choice to finally & completely become a monster

I do think that there are two personalities acting in our villain. As Gandalf says:

Originally Posted by Shadow of the past, FotR

Even Gollum was not wholly ruined. He had proved tougher than even one of the Wise would have guessed -as a hobbit might. There was a little corner of his mind that was still his own, and light came through it, as through a chink in the dark: light out of the past. It was actually pleasant, I think, to hear a kindly voice again, bringing up memories of wind, and trees, and sun on the grass, and such forgotten things. But that, of course, would only make the evil part of him angrier in the end – unless it could be conquered.

Thus, I would say that what Tolkien was trying to portray in Gollum was not a split personality in the sense of multiple personalities of rather equal standing, split from the same root - but a mind crushed by a power greater than it, which has taken under its dominion almost all its willpower. I believe it is safe to say that Smeagol would not have done worse deeds than theft or pranks if he didn't have the ring. If we are to take the Shire as a point of reference for Smeagol's lands too, then killing another hobbit is rather out of the question, and his past wouldn't justify, in my opinion, his going down that road by himself. To be more exact, the two personalities at work would be Smeagol - and the ring's taint on his mind.