When Arthur Schopenhauer read the libretto of “Die Walküre,” the second installment of Wagner’s “Ring” cycle, he found himself discomfited by the goings on in Act I, in which the twin siblings Siegmund and Sieglinde, separated children of the god Wotan, fall madly in love. “You are bride and sister to your brother,” Siegmund exclaims. The music that churns ecstatically in the closing bars indicates that consummation is imminent, with the hero Siegfried as the destined result. Next to the stage direction at the end—“The curtain falls quickly”—Schopenhauer sardonically wrote, “Denn es ist hohe Zeit”—“Because it’s high time.”

Mythic and fantasy narratives gravitate strikingly often toward incestuous themes. “Game of Thrones,” the HBO series that a portion of the planet has been watching, is a case in point. It features not only a sibling affair, between Cersei Lannister and her twin brother Jaime, but also a liaison between the dragon-mother Daenerys and the outcast hero Jon Snow, who, unbeknownst to each other, are aunt and nephew. The latter relationship matches the other great eyebrow-raising romance in the “Ring”—the love of Siegfried and Brünnhilde. Siegfried is Wotan’s grandson; Brünnhilde is his Valkyrie daughter. It’s not clear whether George R. R. Martin, the creator of “Game of Thrones,” has Wagnerian leanings, but the proliferation of “Ring”-like elements in his saga—dragons, dwarves, ravens, magic swords, shape-shifting devices—suggests that, like J. R. R. Tolkien before him, he may owe a few debts to the wizard of Bayreuth.

A formidable array of thinkers have addressed incest stories in ancient and modern literature. Sigmund Freud, Carl Jung, Claude Lévi-Strauss, and Jacques Lacan all scrutinized the primal transgression of Oedipus and Jocasta, linking it to the emergence of the incest taboo and the regulation of human society. Lévi-Strauss, who considered Wagner the “originator of the structural analysis of myth,” widened his inquiry to include the incest of the “Ring”: the fate of the gods and their progeny is tied to a foundational negotiation between nature and culture, the transition from primitive tribalism to a civilized order. A latter-day Lévi-Strauss might take at least a passing interest in “Game of Thrones.” If the “Ring” analogy holds, none of the four principal characters now engaged in intrafamilial intercourse is likely to overcome Westeros’s inherent social contradictions. Crafty dwarves, however, have a way of surviving doom.

The “Ring” is more than a refashioning of myth; from the outset, Wagner intended an allegorical assault on modern capitalist society. In that light, taboo relationships assume a different character: they voice a defiance of bourgeois restrictions on sexuality. In a crucial scene in Act II of “Die Walküre,” which I discussed in an article for the magazine in 2011, Wotan debates changing mores with his wife, Fricka. The god has tried to create a freely acting hero who can win the Ring back from the dragon Fafner without violating prior contractual arrangements. Fricka argues that the union of the twins exposes the corruption of his scheme. Wotan replies: “Age-old custom / is all you can grasp.” He is undoubtedly speaking for the composer, who conducted scandalous affairs, had a fetish for satin, and welcomed gay men into his circle. Wotan’s defense of rebellious love in the face of cold morality resonated with listeners who had to suppress their natural urges and conform to norms, often by way of sham marriages. Early campaigners for gay rights considered Wagner an ally, if not one of their own.

The love of Brünnhilde and Siegfried carries a particularly forceful message. While the pairing certainly has its peculiarities—Lévi-Strauss says that Brünnhilde is a “supermother” to Siegfried, having protected him since birth—its depth of feeling stands in contrast to the calculated marriage contracts of “Götterdämmerung,” in which Brünnhilde becomes an object of exchange. Wagner was no feminist, yet he had many feminist fans, who took inspiration from such ungovernable female characters as Brünnhilde, Isolde, and Kundry, in “Parsifal.” The turn-of-the-century Wagner soprano Lillian Nordica, a campaigner for women’s rights, once said that the world of the stage was the “only place where men and women stand on a perfect equality where there is true comradeship.” At the end of the “Ring,” Brünnhilde accomplishes something greater: as she sets Valhalla ablaze, she is the leading agent of the transformation of the world.

At the same time, Wagner’s fixation on incest came to be seen as a symptom of his decadence. In Élémir Bourges’s 1884 novel, “The Twilight of the Gods,” an aristocratic family is in decline, and one sign of its degeneration is the coupling of two half-siblings, Hans Ulric and Christiane. A scheming Wagnerian soprano has become their father’s mistress, and conceives a plan to destroy the children, who stand in her way. She proposes an amateur performance of “Die Walküre,” with Hans Ulric and Christiane playing the twins. They cannot resist the urge to stay in character, with disastrous results: one shoots himself, the other enters a convent. Thomas Mann took up the same theme in his notorious story “Blood of the Walsungs,” from 1905, which portrays a wealthy Jewish couple so infatuated with Wagner that they have named their twin children Siegmund and Sieglind. After a performance of “Walküre,” the twins indulge in an act of “hasty tumbling” on a bearskin rug. The story caused a scandal because Mann had married into the Pringsheim family, which unmistakably resembled the fictional Aarenholds. Katia, Mann’s wife, had a twin brother named Klaus, to whom Mann also felt some attraction.

All this highlights the most unsettling aspect of incest narratives, which is their appeal to the darker corners of sexual fantasy. When such fantasy breaks into real life, it often occurs in the context of psychological and physical abuse. (Mann’s diaries disturbingly reveal that he gazed with longing at his teen-age son Klaus.) The panting sensuality of Wagner’s music in “Die Walküre” pushes the action into an ill-defined zone between the mythological and the pornographic. The soft-core steaminess of “Game of Thrones” threatens to wipe out the symbolic dimension altogether; there is no judicious fall of the curtain. It’s telling, though, that Cersei and Jaime seem to act out of joyless compulsion, as if all other outlets have been closed off.

Both the “Ring” and “Game of Thrones” are ultimately concerned not with sex but with power. Indeed, in Wagner, supreme power is gained only through the renunciation of love. The notable thing about the “Ring” is that it has no real villains, despite the sinister conspiring of Alberich and his son Hagen. Power itself, incarnated in the Ring, is the enemy. “The Lord of the Rings” and “Game of Thrones,” two latter-day Wagnerian sagas, offer nothing so radical: instead, evil is outsourced to supernatural entities, Sauron and the Night King. This fantasy of an archenemy who stands outside the warring factions of society is a regressive one. If, as many have suggested, the ice-zombie invasion in “Game of Thrones” alludes to the global threat of climate change, there should be some sense that humanity is responsible for the crisis. So far, this is not apparent. The “Ring,” for its part, lets no one escape blame for a catastrophe that is ecological in scope, as Patrice Chéreau’s great 1976 production at Bayreuth made clear. “I longed in my heart for power,” Wotan says in his self-scouring Act II monologue. “I acted unfairly.” He faces Ohnmacht, powerlessness. By the end, Brünnhilde hints, he has found peace.

Once upon a time, in the years around 1900, the “Ring” was not only a world-historical masterpiece of Shakespearean breadth but also a swords-and-sorcery epic, one that sated a great many adolescent imaginations. An amusing shelf of the near-infinite Wagner library is occupied by what might be called young-adult Wagner books, in which authors attempt to bring the operas in line with Victorian mores. Grace Edson Barber’s “Wagner Opera Stories” skips over the entire first act of “Die Walküre,” saying only that Brünnhilde had defended an unnamed “brave friend” who had “not been true to all the laws.” Anna Alice Chapin’s “The Story of the Rheingold” deftly finesses the twins’ bond by claiming that “they loved each other as much as though they had been really brother and sister.” Soon enough, young Wagner fans discovered what was actually going on. The overriding lesson of myth is that its meaning can never be controlled: the Nazis proved as much by reducing Wagner’s intricate philosophical narrative to a cult of Aryan manhood. The more potent the myth, the more fragile the allegory.