Sökmímir or Søkkmímir was a jotun who appears in two sources from Norse mythology, suggesting that he was once a well-known giant in Scandinavia.
In Grímnismál, stanza 50, it appears that Odin killed the giant:
Sviðurr ok Sviðrir
er ek hét at Søkkmímis,
ok dulða ek þann inn alda iötun,
þá er ek Miðviðnis vark
ins mæra burar
So. I deceived the giant
As Svithur and Svithrir of yore;
Of Mithvitnir's son
the slayer I was
When the famed one found his doom.
Svidur and Svidrir
I was at Sökkmimir's called,
and beguiled that ancient Jötun,
when of Midvitnir's
I was the sole destroyer.
He notably appears in Ynglingatal, where subterranean abodes of giants are called Sökkmímir's halls:
þá er í stein
ept dvergi hljóp,
ok salr bjartr
við jöfri gein.
By Diurnir's elfin race,
Who haunt the cliffs and shun day's face,
The valiant Swegde was deceived,
The elf's false words the king believed.
The dauntless hero rushing on,
Passed through the yawning mouth of stone:
It yawned – it shut – the hero fell,
In Saekmime's hall, where giants dwell.