Gollum is quite possibly one of the most tragic characters in the entire Lord of the Rings franchise. Gandalf describes his life as a "sad tale," which is certainly true. From the moment the ring of power first comes into his possession, Gollum walks the tight rope between a corrupted desire to own and possess the evil object, and a desperate longing to be free of its torment. The ring makes him do awful things, including strangling his cousin Deagol to death and disappearing into a hole underneath the goblin tunnels, scorning all sunlight and fresh air and earthly pleasures of his former life.
Frodo is the first character in many hundreds of years who actually relates to Gollum, and sees the pain and suffering that the ring has caused the poor creature, the same pain and suffering that Frodo himself is going through. But by the time Frodo and Sam come into contact with Gollum, he had already sat alone underground with the evil thing in his grasp for nearly 500 years. As is well known, Gollum falls just short of redemption, and despite Frodo’s best efforts, ends up giving in to the temptation of the ring, and dies in the fires of Mount Doom alongside his precious. The question is, if Frodo and Sam had met the poor creature years earlier, would they have been able to save him? Or was he beyond salvation from the very moment the ring came to him?
It is clear throughout both the movies and books that Gollum was not always as cunning and as cruel as he is in the War of the Ring. However, neither was he ever as pure-hearted or as kind-natured as the other hobbits in the stories, for example Samwise, who is known to be particularly loving and loyal. This is, in part, why Samwise and Gollum clash so much, because Sam cannot even fathom the malice and the greed that Gollum demonstrates. He is too good to have ever experienced being as selfish and as threatening as Gollum is. Gollum was always a particularly greedy and self-serving creature, which is a contributing factor in why he was forced out of his home by the other villagers after he found the ring, as they already held no particular love for him. It may also have played a part in why the ring was able to corrupt him so deeply.
Frodo is the first person, possibly in Gollum's entire life (other than his old grandma whom he lived with on the river as a small boy), to ever treat Gollum with true compassion, and to trust him, believing him capable of goodness. Bilbo almost saw the same within him 60 years earlier, during his own adventures to reclaim Erebor with the dwarves. It was this humanity within Gollum, this deep-rooted sadness and loneliness, that made Bilbo spare the creature when he first came across him in the goblin tunnels. Tolkien himself saw Gollum as a cruel and tricky character long before the ring came to him, but knew that somewhere deep in the recesses of his soul, he was capable of more than just this, and could have been changed by a gentle and loving benefactor such as Frodo.
That is why he wrote this scene in the Two Towers, one of the most tragic moments in all of the stories, the moment that shows Gollum at the heart of himself, beneath all the layers of corruption and pain and self-preservation that he has been forced to develop at the hands of the ring. He looks upon Sam and Frodo, sleeping, and seems to debate whether to attack them and take the ring — but instead, reaches out to gently touch Frodo's knee. He is no longer conniving and manipulative, but exhausted and weary. For a moment, he appears simply an old hobbit, described as "an old starved pitiable thing." But the moment is fleeting — Sam wakes, and is immediately suspicious of Gollum's intentions, causing him to withdraw back into that mindset of self-preservation.
So perhaps things could have been different for Gollum, had he met someone who empathized with him before the ring corrupted him so feeply. Perhaps he could have undone all the years of spite and malice that the ring had instilled in him, but thanks to other characters in the books, who only had the best intentions, this was never possible. Sam, for examplem was so desperate to protect Frodo that he treated Gollum always with suspicion and hatred; meanehile, Faramir, who was simply trying to do his best for Gondor, beat and mistreated the creature in the forbidden pool. Gollum never quite actualizes upon the redemption that was just outside his reach, and that is the real tragedy of his character.