Sökkmímir

Sökkmímir or Søkkmímir was a jötunn who appears in two sources from Norse mythology, suggesting that he was once a well-known jötunn in Scandinavia.

In Grímnismál, stanza 50, it appears that Odin killed the jötunn:

He notably appears in Ynglingatal, where subterranean abodes of jötnar are called Sökkmímir's halls: