Regarded as one of Richard Wagner's masterpieces, it is a series of four long works based loosely on characters from Norse sagas. The work described is

Norma is an opera composed by Vincenzo Bellini, not Richard Wagner. It tells the story of a Druid priestess and is renowned for its beautiful melodies, particularly the famous aria "Casta Diva." While it is a significant work in the operatic repertoire, it does not relate to Norse sagas or Wagner's compositions.

Rienzi is an early opera by Wagner that draws inspiration from the historical figure Cola di Rienzi, a medieval Roman leader. Although it showcases Wagner’s growing musical style, it is not part of the Norse saga-inspired works and does not share the same epic narrative scope as Der Ring des Nibelungen.

Tristan und Isolde is another of Wagner's masterpieces, but it centers on a tragic love story rather than the themes of power and destiny found in Der Ring des Nibelungen. This opera is based on the legend of Tristan and Iseult, a tale distinct from the Norse myths that Wagner explored in his cycle.

Der Rosenkavalier is an opera by Richard Strauss, not Wagner. It is a comedy set in 18th-century Vienna and focuses on themes of love and social class, diverging entirely from the epic and mythological context of Wagner's Ring cycle.