Ymir was the first Frost Giant. Odin, Vili and Ve killed him and created the world with his body. He is somewhat akin to the Titans of Greek Mythology in his violent cruelty and the fact that he was overthrown by younger gods.

“From Ymir’s flesh
the earth was formed,
and from his bones the hills,
the heaven from the skull
of that ice-cold giant,
and from his blood the sea.”

-- The Poetic Eddas, The Lay of Vafthrudnir