Satan can mimic a true angel in his appearance. In this manner he can convince individuals to preach the doctrine of Satan while they believe that they are doing the work of the Lord. This is what happened to two anti-Christs in the Book of Mormon. Sherem admitted that he had been deceived by the power of the devil (Jacob 7:18). Korihor said, the devil hath deceived me; for he appeared unto me in the form of an angel, and said unto me: Go and reclaim this people, for they have all gone astray after an unknown God (Alma 30:53). Joseph Smith gave us a key to be able to detect Satan when he appears in this form, If it be the devil as an angel of light, when you ask him to shake hands he will offer you his hand, and you will not feel anything; you may therefore detect him (DC 129:8).