what does it look like?
The Ring seemed to be made simply of gold
One Ring
The Ring seemed to be made simply of gold, but it was completely impervious to damage, even to dragon fire (unlike other rings). 
what's the ring called in lord of the rings The "One Ring" what is its purpose? The One Ring is a central plot element in "The Lord of the Rings", it is a magic ring that grants the wearer invisibility
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One Ring [SEP] Appearance
The Ring seemed to be made simply of gold, but it was completely impervious to damage, even to dragon fire (unlike other rings). It could be destroyed only by throwing it into the pit of the volcanic Mount Doom where it had been forged. Like some lesser rings, but unlike the other Rings of Power, it bore no gem. It could change size, and perhaps its weight, and could suddenly expand to escape from its wearer. Its identity could be determined by placing it in a fire, when it displayed a fiery inscription in the Black Speech that Sauron had devised.