Samuel is notable in the Book of Mormon as he is a Lamanite prophet. Lamanites generally are described as wicked, and most prophets are Nephites.
After attempting to preach to the people in Zarahemla, and being rejected, he was told by revelation to return and prophesy to the people. He was not allowed into the city. In one of the more iconic stories of the Book of Mormon, he preached on the wall of the city, calling the people to repentance for their sins, prophesying about the impending advent of Jesus Christ in the Old World, and warning of the destruction of the Nephite nation. The people in the city tried to kill him by throwing stones and shooting arrows, but he was protected from harm by divine providence.