Back in 1980 I had been a fan of the Marvel comic Thor for twelve years, and of Richard Wagner's Der Ring Des Nibelungen for two years. Thus I was well-placed to appreciate the storyline that began in issue 294 of Thor (cover-dated April 1980), which bears a more-than-passing resemblance to Wagner's magnum opus (a fact heralded in the Bullpen Bulletins for that month: "Thor #294: Beginning this issue - the Quest for the Ring of the Nibelung!").
The story in question, written by Roy Thomas and illustrated by Keith Pollard and Chic Stone, is called 'New Asgards for Old', and is based on the intriguing notion that Ragnarok (the Twilight of the Gods of Norse mythology) is cyclic, occurring at the end of each astrological age of approximately 2150 years. The previous Ragnarok-cycle was the one relating to the traditional Norse gods (the Aesir) that feature in the Icelandic Eddas and in Wagner's Ring. The present cycle is the one relating to the Marvel Comics characters (Asgardians) with the same names as the old Norse gods.
The Ring of the Nibelung, illustrated by Gil Kane. But back in 1980, graphic novels hadn't been invented, and the pages of Thor were the next best thing!
The way in which Roy Thomas contrives to tell the story of The Ring -- pretty faithfully, all things considered -- is to have "our" Thor as a passive observer of the past, watching the events of the previous Ragnarok unfold (except it's Wagner's version he witnesses, not the traditional Eddaic one!). The mapping of Wagner's operas onto the comic books, following on from the beginning of Das Rheingold in issue 294, is as follows:
Issue 295 ('The Price and the Pride') presents the remainder of Das Rheingold, ending with the creation of the Rainbow Bridge by the god Donner (the German rendering of "Thor")... who looks almost exactly like our Thor!
Issue 296 ('From Valhalla a Valkyrie') corresponds to the first two acts of Die Walküre, with the character Siegmund looking suspiciously like Thor (and the valkyrie Brünnhilde looking exactly like the comic-book character Valkyrie!).
Issue 297 ('The Sword of Siegfried') presents the last act of Die Walküre and the first act of Siegfried (and now Siegfried is the one who looks like Thor!).
Issue 298 ('Dragon's Blood'), depicting the second and third acts of Siegfried, is the first instalment to give Wagner a name-check in the credits: "Based on the opera Siegfried by Richard Wagner".
Issue 299 ('Passions and Potions') bears the credit "Based on the opera Götterdämmerung by Richard Wagner"... and it does indeed cram in more than two-thirds of that gigantic opera!
Issue 300 ('Twilight of the Gods') manages to tie up the remainder of Götterdämmerung in its first seven pages. But that's not quite the end of the story...
Strange as it may seem, these issues of Thor weren't Wagner's only comic book appearance in 1980. The Summer 1980 issue of the Marvel magazine Epic (aimed at "Mature Readers") contains an eight page story by P. Craig Russell entitled 'Siegfried and the Dragon', which is credited as coming "from the story by Richard Wagner". As so often with comics aimed at an adult audience, this story is (in my humble opinion) considerably limper than the one meant for younger readers. You can compare the Epic version (upper) and the Thor version (lower) in the following details from their respective splash pages. Somehow I feel Wagner would prefer the latter!