Antichrists throughout history
The teaching against Antichrist is relevant today. John's first letter warns against antichrists and provides guidance on their treatment by the church. This teaching is relevant to all ages.
Around 100AD a sect called the Nassenes came to prominence, as described by Hippolytus of Rome (AD170-235) in his book 'The Refutation of all Heresies'. The inspiration for the sect came from the writings of Mariamne. He claimed to have received 'special knowledge' from James, Jesus' brother. In fact his 'special knowledge' turned out to be Egyptian and Assyrian pagan beliefs repackaged. Mariamne and his followers have the dubious distinction of being the first pseudo-Christian cultists in recorded history. Hippolytus in writing about the Nassenes held the view that '[The] Nassene heresy is the root error from which all other heresies had sprung' (Refutation 5.11.1). The root heresy is that Jesus is not God.**
The young Joseph Smith had a good knowledge of the Bible, apparently rejected the divinity of Christ, proclaimed himself a 'new Mohammed' and founded Mormonism.
Charles Taze Russell was a leader in the Bible Student movement on the 19th century. He apparently rejected the divinity of Christ, and founded the Jehovah's Witnesses. According to Catholic.com1 most 'Witnesses' are ex-Catholics and Protestants.
Mary Baker-Eddy was a student of the Bible. She apparently rejected the divinity of Christ and went on to found the Christian Scientists.
John Thomas 'rediscovered' Bible truth. He rejected the divinity of Christ and went on to found the Christadelphians.
Each of the founders of the above modern 'alternatives' to Christian religion had the same background to that of the antichrists described on the Bible: they all understood the gospel (not least due to their knowledge of the Bible), they rejected the deity of Christ and went on to found a religion which sought to attract followers from true Christianity.