I have a tag I use from time to time: “obscure deities”. The Titan Koios (or Coeus) was famous for being obscure. In the Metamorphoses, the ill-fated Niobe says of him and his daughter Leto:
Now, ask what the reason is for my pride, and then dare to prefer Latona to me, that Titaness, daughter of Coeus, whoever he is. Latona, whom the wide earth once refused even a little piece of ground to give birth on.
(Latona is the Roman name for Leto.) Even in her great access of hubris, the only thing Niobe could say of Coeus/Koios was that no one knew who he was. A quick look at online guides to Greek myth shows that Koios is by no means famous now, but there seems to be a desire to fill out his dossier.
Hyperborea, and the Hyperboreans, seem to have had an enduring life among the ancient Greeks and Romans, even if they couldn’t always agree on where it was. It first intrigued me because of the story that Apollo went there every winter.