Joseph Fielding Smith
“There is no doubt about Satan having great power and that he can appear as an angel of light. In this form he appeared on the banks of the Susquehanna River to oppose the restoration of keys, and was detected by Michael, and his plans were thwarted. Jacob, son of Lehi, in his teachings, stated that if there had been no atonement, our spirits ’…must have become like unto him [Satan], and we become devils, angels to a devil, to be shut out from the presence of our God, and to remain with the father of lies, in misery, like unto himself; yea, to that being who beguiled our first parents, who transformeth himself nigh unto an angel of light, and stirreth up the children of men unto secret combinations of murder and all manner of secret works of darkness.’ Korihor, who tried to deceive the Nephites, admitted that Satan appeared to him as an angel and told him what to teach the people.” (Answers to Gospel Questions, vol. 1, p. 178)
Bruce R. McConkie
“Lucifer does not come personally to every false prophet, as he did to Korihor, any more than the Lord comes personally to every true prophet, as he did to Joseph Smith. Such an appearance--either of God on the one hand or of Satan on the other--is, however, the end result of full devotion to the respective causes involved. In each instance an earthly representative, by obedience to the laws that are ordained, may see the face of the master he serves.” (Millennial Messiah, p. 72)