We, fortunately, or unfortunately are dealing with two quite different Gollums by the time we get to LotR. The original character was simply a casual monster, some sort of odd creature, a member of a species not even human/ hobbit that lived in the deep places of the world. This Gollum was never specifically assigned a designation "good guy" or "bad," though he was still dangerous as he was quite willing to stake Bilbo's life on the outcome of a riddle-game. But, this 1937 version Gollum was a creature of its word, an honourable thing, and he had promised a gift to Bilbo should the hobbit win the game, as he did. The gift was a ring, not yet The Ring, but still a magical ring that conferred both luck and invisibility upon its bearer. Unknown to Gollum, the ring had been lost and then found by Bilbo who, at the end of the riddle-game already had it in his pocket. Unable to give Bilbo the promised ring/ present, Gollum sought honourably to make up for its lack by showing Bilbo the way out of the caves and mines. "Now Gollum had to agree to this, if he was not to cheat. He still very much wanted just to try what the stranger tasted like; but now he had to give up all idea of it." (Annotated Hobbit, p. 130) At last Gollum faithfully led Bilbo to the final passage that opened onto the Goblin's gate and the two politely said "goodbye" before Gollum padded back to his lake and Bilbo braved the Goblins at the door. So, other than a slightly distressing penchant for eating his fellow "speaking" creatures, Gollum comes off as a fairly decent sort in the pre-LotR days.
With the writing of LotR, Tolkien altered the character of Gollum's magic ring, elevating it to its potent position as The One Ring. It now became necessary to alter Gollum's own nature, and make him a far more desperately dangerous, and deceitful creature, a mind-blasted addict whose dope was the Ring. A more suitable "back-history" had to be developed for Gollum, detailing who/ what he had been; how he had possessed himself of the Ring; and how the Ring eventually possessed him, together with the great changes it made in his personality, body, and mind. Gollum, now Smeagol, was made a hobbit, but the back story was not sufficiently detailed in LotR to give us a chance to class him (in his pre-Ring days) as a "bad" hobbit, like Lotho Pimple, Lobelia, Ted Sandyman, or simply a regular "good" hobbit (like Samwise) who will later be vastly perverted by the Ring. It is perhaps somewhat indicative of his originally "bad" nature that the mere, first sight of the Ring calls so strongly upon some answering evil in Smeagol, that, before he even touches the thing, or wears it, it corrupts him to an immediate act of murder. Had two "regular" or good hobbits come upon the Ring by chance, say Merry and Pippin, would the result have been the prompt murder of one of them by the other? So, I think we are fairly safe in assuming that there was something "wrong" with Smeagol the hobbit from the beginning, some character flaw that left him particularly vulnerable to the Ring's seduction and control.
Still, perhaps because there were two Gollums, the 1937, dangerous but honourable creature, and the LotR degraded addicted character, the final Gollum comes out looking schizophrenic -- he is sometimes motivated by honourable intentions (as was the 1937 Gollum), but now, in LotR, he is sometimes overpowered by his own desires and the rot the Ring has created in his brain. Sometimes he is an object that solicits our pity, sometimes he is a hateful bundle of sheer malice. I think Tolkien's real genius shines out here, he keeps us ever in suspense with Smeagol/ Gollum, never letting us become comfortable with the ever-changing character, never letting us resolve the ambiguities that surround him, never letting us fully assign him a role that can distinctly be said to be "evil" or "good." This constant tension of suspended judgment makes Gollum the most memorable and vitally alive of all Tolkien's characters, or so I believe.
Here is a definition from Wikipedia:
