Elijah was the prophet who tried to restore the concept of God in the northern Jewish kingdom.  He was the prophet of Mount Carmel.  He secluded himself for a time in solitude.  Denounced Ahab for the murder of the Naboths; he tore down altars of Baal and demolished idols.  The Father spoke through Elijah and other prophets like him. 
Elijah turned Yahweh into Elohim; he turned an agrarian problem into a moral one; he was the one who initiated the passage from the polytheism of the many Baals to the monotheism of Yahweh.  Changed the Yahweh-Baal controversy from land to religion.  Currently he is one of the 24 Jerusem counselors, number 13.  Peter thought he saw Elijah in the transfiguration of Jesus, although the one he actually saw is Father Melchizedek of Nebadon.  The secret writings of Elijah and other prophets are what began the Old Testament.  He was a translated soul of brilliant spiritual achievement; that is, that he did not suffer the normal death. 
John adopted Elijah's dress and method.  Denied that he was Elijah returned.  He firmly believed in Elijah's return and lingered in retreat for 2 years in anticipation of that return.  Jesus referred to John as Elijah, following the custom of his time of considering Elijah to be the forerunner of the Messiah. 
See also: UB 135:6.3.