Korihor is the second Antichrist in the Book of Mormon. See the video above and read Alma 30: 6-60.
In a nutshell, Korihor began teaching his particular philosophy that countered the true Gospel of Christ. He was able to persuade others to adopt it. Because the law only punished action, not belief, there wasn't much that could be done about him. The Ammonites wouldn't listen to him and had him ejected from their lands. Korihor went on to greener pastures. He contended with secular and church leaders demanding that he be given a sign from God. He was struck dumb. He asked for his punishment to be reversed insisting he was a changed man. He was refused. He took up life as a beggar and died in an accident.
What is interesting for our purposes is what Korihor was teaching. Many of his philosophies are present today:
There is no Christ.
No one can know the future.
So-called "prophecies" are just foolish traditions.
You can't know something unless you see it.
People who believe in religion are mentally deranged.
We control our lives here. There is no influence from any other power.
There isn't any "sin" per se. You can do what you want to do.
Religion isn't freeing. It's bondage.
Religious leaders are just trying to exert power and authority over you and keep you ignorant.
You can't know if something is true or not.
You can't know Christ will come.
Religious leaders are just trying to oppress people and get rich off of them.
Religious leaders just like directing people based on their own whims.
God doesn't exist now and never has.
I'll evaluate the modern relevance of Korihor's teachings and tactics in future posts.