E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
rendered the wearer invisible. Gygs, the Lydian, is the person to whom Candauls showed his wife naked. According to Plato, Gygs descended into a chasm of the earth, where he found a brazen horse; opening the sides of the animal, he found the carcase of a man, from whose finger he drew off a brazen ring which rendered him invisible, and by means of this ring he entered into the kings chamber and murdered him.
Why, did you think that you had Gygs ring,
Or the herb that gives invisibility [fern-seed]?
Beaumont and Fletcher: Fair Maid of the Inn, i. 1.
The wealth of Gygs. Gygs was a Lydian king, who married Nyssia, the young widow of Candauls, and reigned thirty-eight years. He amassed such wealth that his name became proverbial. (Reigned B.C. 716678.)