In Sumerian mythology, EN.LIL was the second most powerful God of the Pantheon. His name meant "Lord of Airspace." He was the prototype and father of the later storm gods that were to head the pantheons of the ancient world.
He was Anu's eldest son, born at his father's heavenly abode. But at some point in the earliest times, he descended to Earth, and was thus the principal God of Heaven and Earth. When the Gods met in Assembly at the Heavenly abode, Enlil presided alongside his father. When the Gods met for Assembly on Earth, they met at Enlil's court in the divine precinct of Nippur. (Z. Sitchin, the Twelfth Planet)
Enlil's wife was Ninlil (who before the marriage was called Sud). Together they had a son, Nanna (or Nannar) who is also known as Zu, Sin or Suen. He was Enlil's oldest son. However, Enlil also had a son later on with his half-sister Ninhursag. This son was called Ninurta, and was the youngest son. But because of Sumerian succession rules Ninurta was to become the successor of Enlil, as both his parents were children of Anu. Nanna didn't like that and led a mutiny but finally lost to his younger brother. (Later on however, Enki's son Marduk would become the supreme deity).
Enlil was the half-brother of Enki. Both were sons of Anu, "each claiming to be the firstborn, which caused each to believe he was the ruling deity. This conflict is thought to be the source of many later conflicts between the gods." (PoL)
Enlil is also the archetype of the severe, punishing god, who doesn't like the humans too much. When e.g. the Gods knew that the Great Flood was coming, Enlil decided not to warn mankind, because he wanted them to perish.

Personally, I believe Enlil represents both the Lyran and the Pleiadian interventions on Earth. The fact that Enlil often is represented by seven stars only tends to enhance this belief. (Another name for the Pleiades is the "seven sisters").
Other researchers, however, think Enlil represents the Draconian presence on Earth. [Matthew].