Some people do not believe that there are any devils

Heber C. Kimball (First Presidency)
It is written, “resist the devil and he will flee from you.” Some people do not believe that there are any devils. There are thousands of evil spirits that are just as ugly as evil can make them. The wicked die, and their spirits remain not far from where their tabernacles are. When I was in England, twenty-eight years ago next June, I saw more devils than there are persons here to-day; they came upon me with an intention to destroy me; they are the spirits of wicked men who, while in the flesh, were opposed to God and his purposes. I saw them with what we call the spiritual eyes, but what is in reality the natural eye. The atmosphere of many parts of these mountains is doubtless the abode of the spirits of Gadianton robbers, whose spirits are as wicked as hell, and who would kill Jesus Christ and every Apostle and righteous person that ever lived if they had the power. It is by the influence of such wicked spirits that men and women are all the time tempted to tell little lies, to steal a little, to take advantage of their neighbor a little, and they tell us there is no harm in it. It is by the influence and power of evil spirits that the minds of men are prejudiced against each other, until they are led to do each other an injury, and sometimes to kill each other. (Journal of Discourses, 11:84-85)