Emrakul is the greatest of the three Eldrazi titans, horrible Lovecraftian monstrosities born in the space between planes, the Blind Eternities. These beings feed on entire universes for sustenance, leaving nothing behind except empty husks of a reality. Each of the three Eldrazi titans has a lesser lineage they use as sort of a "digestive system" to speed up the consumption of a plane; usually of its life forms.