When Skadi came to confront the Aesir for killing her father, they offered her three things: one, to make her laugh, two, that she be allowed to chose a husband from among the Aesir, three, that her father’s eyes would be cast into the heavens as stars. The fierce frost giantess accepted and winter’s wrath was turned aside.
 
“From Elivagar sprang venom drops, which grew till they became a Jötun; but sparks flew from the south-world: to the ice the fire gave life.”

-- The Poetic Eddas, The Lay of Vafthrudnir