Richard Wagner's Ring was only one version of a vast series of sagas and myths.  While there was nearly always a dragon, there was not necessarily always a Ring in these sagas.  There was often a hero, such as Sigurd or Siegfried, his wife or romantic interest, such as Kriemhild, and a warrior princess such as Brynhild, who was often his true love or part of a love triangle.
Wagner borrowed from the Poetic and the Prose Old Norse Edda Sagas, the Old Norse Volsung Saga, the Middle High German Nibelungenleid saga, and the Old Norse Thidreks Saga.
Mythology tended to be filled with strange plot twists and non-sequitors. Wagner certainly excelled at carrying on this tradition. While we could live with this in opera, we would not be so forgiving for cinema.
Many variations of these sagas have been published in books on mythology, by Arthur Rackham early in the Twentieth Century, and recently, even in comic books, such as Dark Horse Comics and DC Comics.
Fritz Lang produced the first cinematic version in 1924, titled Die Nibelungen, which did not feature a Ring. However, it did have a treasure hoard containing an enchanted sword, which was not associated with the dragon. It also had what what likely the first movie sequel.
The most recent cinematic version was the 2004 film, Ring of the Nibelungs.  In an age of slam-bang special effects, people no longer like movies with understated characters and slow, deliberate plotting, especially tragedies, considering that Siegfried is always murdered by Hagen.
The most famous television adaptation must have been episodes 119-121, season six of Xena: The Warrior Princess, where many of the same characters from Wagner's Ring were interwoven into the Xena universe.

We saw Wagner's Opera series, Der Ring des Nibelungen, as four separate performances from August 15 to August 20, 2005.  I am making my comments and observations of this experience in five following web pages.

Unlike more modern works based upon epic mythology, Wagner's characters were not exactly black and white, good and evil.  Most of the characters were, in fact, somewhat amoral, reflecting Wagner's personal life.  The later tetralogy of J.R.R. Tolkien (The Hobbit plus Lord of the Rings,) borrowed heavily from Wagner, but framed the characters more in more typical good versus evil context.  Tolkien did not like moral ambiguity; for instance, there was not even a hint that there was anything remotely good about an Orc or an Uruk-hai.

There were only so many versions of epic mythology to draw from.  Wagner did a kind of cut and paste from several related Norse and Germanic legends.  It should not be surprising that there was a lot of correlation between Der Ring des Nibelungen and epics such as Tolkien's Lord of the Rings and George Lukas' Star Wars.

Comparisons:

One might ask what relevance all this might have to our own lives in the modern world.  After all, events taking place in a 400 A.D. culture can seem quite dated.   Yet, there are currently a lot of good people doing bad things, and a straying from or bending of the word of the law, that are disturbingly similar to events in Der Ring des Nibelungen.

Prologue
Das Rheingold
Die Walküre
Siegfried
Götterdämmerung