Ymir

Ymir is the embodiment of primeval chaos, and first jötunn to exist in Norse mythology.

Description
Ymir comes into being when fire and ice poured down into cosmological abyss. Before him there was nothing. Soon after followed primordial cow, Audhumla, whose milk Ymir fed upon.

Ymir continues to steadily grow larger and larger. He breeds asexually. First female and first male jötnar are born from the sweat of his armpits, and another six headed jötunn sprangs forth from the soles of his feet. This makes him the ancestor of all jötnar, as well as the gods of Norse mythology, who often shared bloodline with jötnar.

After Odin and his brothers were born, they were alarmed by Ymir's unrestricted growth and killed him. From his body they crafted the physical world. His blood became the sea (which nearly drowned all the other jötnar) and his flesh were the lands. His eyebrows formed the area wherein humans lived.

Audhumla and Búri
Audhumla was the second being in existence. From her teats ran four great rivers of milk. The rivers were source of nourishment for Ymir. Audhumla herself feeds on the salty rimestones by licking them. Continuous licking over three days slowly exposes another being into existence. This is Búri, the ancestor of Norse gods. He is also known as the progenitor god.

Not much is known of him, except that he is the ancestor of Norse gods same way as Ymir is the ancestor of jötnar. It's unknown how he begat his son Borr. Either Borr came into being asexually like Ymir's progeny, or Búri had intercourse with a jötunn that had come from Ymir.