Eru (
the One), also called 
Ilúvatar (
the Father of All or 
the Lord of All) is the name in the works of 
J.R.R. Tolkien for the supreme 
God, the creator of the angels (
Ainur), the universe (
Eä), and its inhabitants. He is a single male omnipotent creator. Eru is an important part of the stories of 
The Silmarillion but is not mentioned by name in Tolkien's most famous works, 
The Hobbit and 
The Lord of the Rings.  (He is alluded to as "the One" in the part of LotR's Appendix A that speaks of the downfall of 
Númenor.)
 
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