The Existence of Satan

Church Educational System
A corollary to the pernicious falsehood that God is dead is the equally pernicious doctrine that there is no devil. Satan himself is the father of both of these lies. To believe them is to surrender to him. Such surrender has always led, is leading now, and will continue to lead men to destruction.

Latter-day Saints know that there is a God. With like certainty, they know that Satan lives, that he is a powerful personage of spirit, the archenemy of God, of man, and of righteousness.

The reality of the existence of both God and the devil is conclusively established by the scriptures and by human experience.

(Marion G. Romney, Ensign, June 1971, p. 35)

Book of Mormon Student Manual (1996 Edition)