Smeagol A.K.A Gollum survives the fall into the Mount Doom. How?? It's somehow like this - When gollum is falling, he grabs a ledge of black stone, ring in his hand. He pulls himself up, sits on the ledge when he notices that the ring is standing on its own on the ledge. He tries to pick it but fails to do so as the ring is fused with the stone. After many futile attempts, he manages to pry the ring. But a small piece of rock is still clinging to the ring. Being too tired he leaves it be.
The ring loses it's power due to coming too close to the fires which forged it. But as the ring itself is pure evil it leaves the traces of evilness by sharing a new power (of sinister resurrection) into the stone clinging to it . And when gollum wears the stone infused ring, somehow the evil fire fuses the heart of gollum with the ring to protect itself. So as long as the ring is intact, the gollum lives. And the 'preciouss' becomes 'more preciouss' to gollum than his own life. Gollum leaves the middle earth in a small boat towards the lands beyond.
After many years, surviving on fishes, gollum comes ashore into an unknown land (Our earth). Avoiding attention of the people, he resides in a forest, eating rabbits and fishes from river.
Centuries pass and the ring remains hidden with gollum (gollum customizes it by honing and tinkering). One day a wizard (Cadmus Peverell) crosses path with gollum and instantly becomes infatuated by the alluring power of ring. He tricks gollum by using magic and steals the ring.
Years pass and so is the ring passed from heir to heir in peverell family to the gaunt family (having come into the Gaunt line from an heiress of the Peverells). Until one day it is stolen from Morfin Gaunt by Tom Riddle A.K.A Voldemort while Tom framed Morfin for the murders of the Riddle family.
And after the events of Deathly Hallows, the ring remains buried in the forbidden forest. One day an female house elf (actually dobby's gf) who works in the hogwarts kitchen, comes across the ring in the forbidden forest.
Recognizing the ring as the resurrection stone, she is obsessed by the desire to bring Dobby back. So she digs up Dobby's body (Now starting to rot) from the grave and resurrects dobby, who looks as decrepit like a zombie now as half of his body is rotten.
Being in touch with an elf (related to dark elves - the race who created the ring in the first place ), the ring awakes and regains its power of luring people and beings alike. Dobby picks the ring and wears it muttering, "My Preciouss"
In the meantime, Gollum finds his way into london being drawn towards the woken power of ring.
Tracing the ring to dobby, he finally confronts Dobby. Both want the ring but only one could have it..... And so starts 'Dobby Vs. Gollum' Round one.....