In Norse mythology, Ragnarök (ˈræɡnəˌrɒk,_ˈrɑːɡ-; Ragnarǫk) is a foretold series of impending events, including a great battle in which numerous great Norse mythological figures will perish (including the gods Odin, Thor, Týr, Freyr, Heimdall, and Loki); it will entail a catastrophic series of natural disasters, including the burning of the world, and culminate in the submersion of the world underwater. After these events, the world will rise again, cleansed and fertile, the surviving and returning gods will meet, and the world will be repopulated by two human survivors, Líf and Lífþrasir. Ragnarök is an important event in Norse mythology and has been the subject of scholarly discourse and theory in the history of Germanic studies. The event is attested primarily in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. In the Prose Edda and in a single poem in the Poetic Edda, the event is referred to as Ragnarøkkr, a usage popularised by 19th-century composer Richard Wagner with the title of the last of his Der Ring des Nibelungen operas, Götterdämmerung (1876), which is "Twilight of the Gods" in German. The Old Norse compound word ragnarok has a long history of interpretation. Its first element is clear: ragna, the genitive plural of regin (n. pl.) 'the ruling powers, gods.' The second element is more problematic, as it occurs in two variants, -rök and -røkkr. Writing in the early 20th century, philologist Geir Zoëga treats the two forms as two separate compounds, glossing ragnarök as 'the doom or destruction of the gods' and ragnarøkkr as 'the twilight of the gods.' The plural noun rök has several meanings, including 'development', 'origin', 'cause', 'relation', 'fate.' The word ragnarök as a whole is then usually interpreted as the 'final destiny of the gods.' The singular form ragnarøk(k)r is found in a stanza of the Poetic Edda poem Lokasenna, and in the Prose Edda.