If Herodotus' earlier account of Persian aitia is orderly and sober, his genealogy of Lydian kings is convoluted and chaotic. Herodotus' motives here, however, are artistic rather than scientific and objective, for he wants, first of all, to make a pointed contrast between the clear, organized sequence of fictional heroines and the chronologically confused list of real kings. He also wants to provide a suitably heroic and dramatic introduction for the story of Gyges and Candaules, two of the cheif actors in the story he is about to tell. Candaules must come onstage freighted with his numerous and noble ancestors, for the usurper Gyges must seem to violate this unbroken dynastic tradition, a sin for which his descendant Croesus in the fifth generation must pay. Croesus, just as Candaules is the last Heraclid king of Lydia, will be the last Mermnad, indeed the last king of all. The story of Gyges thus begins in a mood of some fateful foreboding, for Herodotus portrays the shift in the kingship of Lydia from the Heraclids to the Mermnads as a momenus event."
Stewart Flory The Archaic Smile of Herodotus (1941) p.29-30