Gyges (, ; Greek: ; Lydian? Kuka?; fl. 7th century BC) was the founder of the Mermnad dynasty of Lydian kings. The dates of his reign are uncertain but have been tentatively estimated as c. 687 - c. 652 BC. He was a bodyguard of his predecessor Candaules whom he assassinated in order to seize the throne. His action was approved by the Delphic Oracle and that decision prevented civil war in Lydia. Once established on the throne, Gyges devoted himself to consolidating his kingdom and making it a military power.
He captured Colophon, Magnesia on the Maeander, and probably also Sipylus, whose successor was to become the city also named Magnesia in later records. Smyrna was besieged, and to the north, the Troad was brought under Lydian control. Gyges pushed back the Cimmerians, who had ravaged Asia Minor and caused the fall of Phrygia. During his campaigns against the Cimmerians, he failed to engage the help of the Assyrians and turned instead to Ancient Egypt, sending his Carian troops to assist Psammetichus. Gyges later fell in a battle against the Cimmerii under Dugdamme, and was succeeded by his son Ardys of Lydia.
The name of the Lydian king is attested many times in Greek transmission. In addition, the annals of the Assyrian king Ashurbanipal, refer several times to Gu(g)gu, king of Luddi, to be identified with Gyges, king of the Lydians.  Many Bible scholars believe that Gyges of Lydia was the Biblical figure of Gog, ruler of Magog, who is mentioned in the Book of Ezekiel and the Book of Revelation. This name is probably of Carian origin, being cognate with Hittite ?ua-, Luwian /huha-/ and Lycian xuga- 'grandfather'. The Carian name quq is attested as in Greek transmission.  This etymology correlates with the intrusive, probably Carian origin of the Mermnad dynasty in Lydia. 
Authors throughout ancient history have told differing stories of Gyges' rise to power, which considerably vary in detail, but virtually all involve Gyges seizing the throne after killing the king, Candaules, and marrying Candaules' widow.
The main source for Gyges is Herodotus, whose account may be traced to the poet Archilochus of Paros. In this, Gyges was a bodyguard of Candaules, who believed his wife to be the most beautiful woman on Earth. He insisted upon Gyges seeing his wife disrobed and the betrayal so enraged her that she afterwards gave Gyges the choice of murdering her husband and making himself king, or of being put to death himself.
Herodotus goes on to record how Gyges plied the Oracle with numerous gifts, notably six mixing bowls minted of gold extracted from the Pactolus river weighing thirty talents. The Oracle confirmed Gyges as the rightful king of Lydia and gave moral support to the Lydians in their conflict with the Ionians. The priestess nevertheless declared that the dynasty of Gyges would fall in the fifth generation. This prediction was later fulfilled when Gyges' fourth descendant, Croesus, lost the kingdom as a result of attacking the Achaemenid Empire of Cyrus the Great.
Nicolaus of Damascus supplies his own version of the story that is quite different from both Herodotus and Plato. It involves a multi-generational curse by an old King Ardys of Lydia, because his trusted advisor Dascylus was murdered by Ardys' son named Sadyattes (or Adyattes). This Sadyattes was jealous of Dascylus' growing power. The murderers were never discovered, so King Ardys issued a curse upon them.
Dascylus' wife, being then pregnant, escapes to Phrygia (her home), and gives birth to a son, also named Dascylus. Later this Dascylus has a son Gyges who, as a young man arrives to Lydia and is recognized by the king for his outstanding abilities. He is appointed to the royal bodyguard.
Gyges soon became a favourite of Candaules and was dispatched by him to fetch Tudo, the daughter of Arnossus of Mysia, whom the Lydian king wished to make his queen. On the way Gyges fell in love with Tudo, who complained to Sadyates of his conduct. Forewarned that the king intended to punish him with death, Gyges assassinated Candaules in the night and seized the throne. According to Plutarch, Gyges seized power with the help of Arselis of Mylasa, the captain of the Lydian bodyguard, whom he had won over to his cause.
Several monarchs of Asia Minor in the Archaic Period, at the height of the influence of the Oracle of Delphi, bolstered their claims to rule through oracles from the Pythia. Herodotus relates that Gyges ascended the throne following a Delphic oracle, which convinced the Lydians to accept him. However, the Pythia had also predicted that the revenge of the Heracleidae would fall upon his fifth descendant. For this oracle Gyges rewarded the oracle with precious ex-votos: six golden kraters were offered to the sanctuary of Apollo. They weighed thirty talents. At the time of Herodotus these kraters were displayed in the Treasury of Corinth. He dedicated other more precious ex-votos, made of gold and silver, which are not, however, mentioned in detail.
Nevertheless, Herodotus seems to have added the detail about the Delphic oracle, and the prediction about the fifth descendant of Gyges who will be revenged by the Heracleidae as a way to account for the fall of King Croesus of Lydia, who belonged to the Mermnadae dynasty.
Once established on the throne, Gyges devoted himself to consolidating his kingdom and making it a military power, although exactly how far the Lydian kingdom extended under his reign is difficult to ascertain.
He captured Colophon, already largely Lydianized in tastes and customs and Magnesia on the Maeander, the only other Aeolian colony in the largely Ionian southern Aegean coast of Anatolia, and probably also Sipylus, whose successor was to become the city also named Magnesia in later records. Smyrna was besieged and alliances were entered into with Ephesus and Miletus. To the north, the Troad was brought under Lydian control.
The armies of Gyges pushed back the Cimmerians, who had ravaged Asia Minor and caused the fall of Phrygia. During his campaigns against the Cimmerians, an embassy was sent to Ashurbanipal at Nineveh in the hope of obtaining his help against the Cimmerians. But the Assyrians were otherwise engaged, and Gyges turned to Ancient Egypt, sending his faithful Carian troops along with Ionian mercenaries to assist Psammetichus in shaking off the Assyrian yoke.
Gyges later fell in a battle against the Cimmerii under Dugdamme (called Lygdamis by Strabo i. 3. 21--"who probably mistook the Greek Delta ? for a Lambda ?"), who had previously advanced as far as the town of Sardis. Gyges was succeeded by his son Ardys of Lydia.
Like many kings of early antiquity, including Midas of Phrygia and even the more historically documented Alexander the Great, Gyges was subject to mythologizing. The motives for such stories are many; one possibility is that the myths embody religious beliefs or practices.
In the second book of Plato's philosophical work The Republic, Glaucon recounts the story of the Ring of Gyges to Socrates, using it to illustrate a point about human nature. Some scholars have suggested that Plato's story was based on a now-lost older version of the myth, while others argue that Plato invented it himself, using elements from Herodotus's story of Gyges. It told of a man named Gyges who lived in Lydia, an area in modern Turkey. He was a shepherd for the king of that land. One day, there was an earthquake while Gyges was out in the fields, and he noticed that a new cave had opened up in a rock face. When he went in to see what was there, he noticed a gold ring on the finger of a former giant king who had been buried in the cave, in an iron horse with a window in its side. He took the ring away with him and soon discovered that it allowed the wearer to become invisible. The next time he went to the palace to give the king a report about his sheep, he put the ring on, seduced the queen, killed the king, and took control of the palace.
In The Republic, Glaucon argues that men are inherently unjust, and are only restrained from unjust behavior by the fetters of law and society. In Glaucon's view, unlimited power blurs the difference between just and unjust men. "Suppose there were two such magic rings," he tells Socrates, "and the just [man] put on one of them and the unjust the other; no man can be imagined to be of such an iron nature that he would stand fast in justice. No man would keep his hands off what was not his own when he could safely take what he liked out of the market or go into houses and lie with anyone at his pleasure, or kill or release from prison whom he would, and in all respects be like a god among men. Then the actions of the just would be as the actions of the unjust; they would both come at last to the same point." Socrates concludes, however, that a truly just man is not a slave to his appetites, so that the opportunities afforded by the ring would not tempt him to abandon his principles.
It is usually thought that these two stories are based on older sources, either two different versions of the story of Gyges or, as K. F. Smith argued, one single longer version of the story, which served as the source for both authors. A third possibility has also been raised: Andrew Laird has recently argued that Plato largely invented his version of the story, inspired primarily by his reading of Herodotus' version.