Smeagol was an ordinary looking hobbit(?) until he took the ring from Deagol.
Why did his body and mind change into the 'Gollum' creature?
The simple answer is "the One Ring", both directly and by Gollum's long life spent in trying conditions.
Gollum lived for many times longer than the usual Hobbit - spending close to 500 years under the Misty Mountains.
- TA 2430 - The approximate birth year of Sméagol.
- TA 2463 - Sméagol (later known as Gollum) becomes the fourth master of the One Ring, after killing his cousin Déagol.
- July, TA 2941 - Bilbo Baggins obtains the One Ring; the White Council drives Sauron out of Dol Guldur.
Dates sourced from Appendix B of the Lord of the Rings.
Over those centuries his mind and body degenerated into Gollum, partly because of the stress of living alone in caves all the time but also because of the effects of the Ring. We know this because we see the same effect on Bilbo in the Fellowship of the Ring as he goes to give up the Ring, both physically:
"Why, I feel all thin, sort of stretched, if you know what I mean: like butter that has been scraped over too much bread."
'If I am it is your fault,' said Bilbo. 'It is mine, I tell you. My own. My precious. Yes, my precious.' The wizard's face remained grave and attentive, and only a flicker in his deep eyes showed that he was startled and indeed alarmed. 'It has been called that before,' he said, 'but not by you.'
'Well, if you want my ring yourself, say so!' cried Bilbo. 'But you won't get it. I won't give my precious away, I tell you.' His hand strayed to the hilt of his small sword.
Smeagol turned into Gollum because he had the ring by himself for to long. In a way, it "possessed" Smeagol. If you were to live forever unless someone killed you, and you lived in an underground cave with no sunlight, eating raw fish, wearing a possessed ring, decaying… you'd get Gollum
correct me if I am wrong but this is what I thought, that rings played on aspects that someone had? All the rings were crafted mainly to enhance the user's native power, rather than conferring new powers on them. The dwarven rings helped the owner to amass gold, and the elven rings helped the owner to preserve things. The one ring played on Sméagol’s deceptiveness transforming him from something who was handsome, into an evil troll?
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