“Regin is a good smith,
But to few is he faithful.”
Týr is a folk metal band from the Faroe Islands.
The Faroes are a territory of the Kingdom of Denmark, located between Great Britain and Iceland.

Via Wikimedia Commons. Used under Creative Commons Attribution-Share Alike 4.0 International license.
Regin Smiður, from their 2003 album Eric the Red is, like many of their songs, based on traditional Faroese ballads known as kvæði, themselves drawing on famous episodes from Scandinavian history or mythology.
Notably, actual kvæði have dozens or even hundreds of verses and a repeating chorus. You get a sense of that in Týr’s traditionally-inspired songs, but for obvious reasons, they’re pretty heavily abridged.
The title Regin Smiður translates to “Regin (Black)Smith.” Incidentally, ‘ð’, the letter Eth is historically pronounced as a th sound — though this is apparently not the case in modern Faroese, where it is largely still retained for primarily etymological reasons.
All of this is to say, the relationship between ‘Smiður‘ and ‘smith’ becomes pretty clear.
Regin is a major figure in the Völsunga saga, the Norse version of the same story that inspired Wagner‘s Ring Cycle.
As is often the case with mythology, there are variations based on language and geography, but the short version is that the hero Sigmund is slain treacherously by his rival Hunding. Sigmund is ultimately avenged by his other son Helgi, who because of this act, comes to be known as Helgi Hundingsbani (that is ‘Hunding’s Bane’; the Slayer of Hunding) — Helgi isn’t a major figure in the Völsunga Saga, but does feature prominently in his own myth cycle — doubly so because he’s said to have reincarnated and had subsequent adventures in his new lifetimes at least twice.
Regin Smiður is primarily concerned with the death of Sigmund, though the chorus does hint at the later adventures of his other son Sigurd, who at Regin’s urging will slay the dragon Fafnir — Regin’s own brother transformed into a monstrous form to guard his hoard of gold.
That Regin is “to few faithful” is a reference to the fact that Regin tries to betray Sigurd (despite being his foster father) and claim the gold for himself.
The gold is, of course, cursed and Sigurd’s subsequent misfortunes because of it form the bulk of the Völsunga saga, though this is left unsaid in Týr’s version of the ballad, which you can listen to here:
Incidentally, Tolkien did a version of the story in alliterative verse which was published posthumously as The Legend of Sigurd and Gudrún – which is probably my favourite non Middle-earth thing in Tolkien’s body of work.
To recap, the first piece of Music to Write Realmgard to was The Sword’s Tres Brujas. You can check out my write-up here: