Eru is a fictional character from J.R.R. Tolkien's legendarium, primarily featured in "The Silmarillion." He is also known as Eru Ilúvatar, the supreme deity and creator of the universe. Eru is responsible for the creation of all beings, including the Ainur, who are powerful spiritual entities that assist him in shaping the world. In Tolkien's mythology, Eru's creation begins with the Music of the Ainur, a cosmic symphony that leads to the formation of Arda, the world. Eru's influence is central to the themes of free will and the struggle between good and evil throughout Tolkien's works.