A magic ring is a fictional piece of jewelry, usually a finger ring, that is purported to have supernatural properties or powers. It appears frequently in fantasy and fairy tales. Magic rings are found in the folklore of every country where rings are worn. Some magic rings can endow the wearer with a variety of abilities including invisibility and immortality. Others can grant wishes or spells such as neverending love and happiness. Sometimes, magic rings can be cursed, as in the mythical ring that was recovered by Sigurd from the hoard of the dragon Fafnir in Norse mythology(pp 14, 57–59) or the fictional ring that features in The Lord of the Rings. More often, however, they are featured as forces for good, or as a neutral tool whose value is dependent upon the wearer.
A finger ring is a convenient choice for a magic item: It is ornamental, distinctive and often unique, a commonly worn item, of a shape that is often endowed with mystical properties (circular), can carry an enchanted stone, and is usually worn on a finger, which can be easily pointed at a target.
Translated from Old Norse with an introduction