We read about many people in the BoM who denied Christ, but there are three persons who stand out as "anti-Christs", who go around among the people and actively preach against His coming. Here's a short summary/analysis:
Sherem (Jacob 7) is preaching that a belief in Christ is distracting the people from keeping the Law of Moses and that "no man knoweth of such things; for he cannot tell of things to come". Ironically, the Law of Moses was "a shadow of those things which are to come" (Mosiah 16:14).
Nehor (Alma 1) is preaching that priests and teachers should become popular and that "all mankind should be saved at the last day". It doesn't explicitly say in Alma 1 that he denied the coming of Christ, but it becomes clear as we read about other people later who practice his religion. See for instance Alma 21:4-8. In verse 8, we read: "We do not believe that thou knowest of things to come".
Korihor (Alma 30) is preaching that there should be no Christ, "for no man can know of anything which is to come" and "that when a man was dead, that was the end thereof". He even says there is no God.
Observations:
- All three deny the coming of Christ, arguing that it's impossible to know anything about the future.
- There is a progression from religiosity to atheism: Sherem wanted the people to get back on track, the Law of Moses being the "right way". Nehor believes that everyone will be saved anyway, so we are not responsible to God for our actions. Korihor denies the very existence of a God.
- Perhaps Satan does not worry too much about what people believe as long as they don't believe in Christ? Except for denying the coming of Christ, Sherem, Nehor and Korihor all gave different messages, perhaps what the people around them at the time were the most likely to receive. It didn't really matter as long as it led them away from Christ.