There is a mis-conception we often hear, that an antichrist (as in only one) is coming at some point, and that things will get really bad when "he" comes. There is another mis-conception that an antichrist (as in only one) has already come. There is a further misconception that Satan is "the" (as in only one) antichrist himself. While there is no way to discuss the antichrist fully in this article, let's examine scripture which will show that none of the above are true.
In my youth, people used to say "the" antichrist (as in only one) was probably Adolph Hitler, as if the antichrist described in the Bible had already come and gone. I don't think you would get much argument that Hitler fit the bill, that part would be correct, but to say he was the only one, would go against scripture, and there have been others just as bad as Hitler. We will show in a minute that antichrists don't have to be narcissistic murdering tyrants like Hitler to be an antichrist, nor do they have to be commissioned by Satan, "marked by Satan with 666", as some would chose to believe.
In Matthew 24:4-5 Jesus said "many" would come in His name and deceive many. Matthew 24:11-12 Christ said false prophets (plural) would rise up and deceive many. ""False christs" and "false prophets" will arise" Jesus warned in Matthew 23:24-25. "Take heed that you not be deceived. For many will come in My name, saying, 'I am He,' and, 'The time has drawn near.' Therefore do not go after them" Jesus warned in Luke 21:8. So when we talk about antichrists, Jesus painted us a good picture of how to recognize many of them. Certainly all who oppose Christ didn't claim to be Him, and many don't come in His name, they oppose Him in other ways.
1 John 2:18, 2:22, 4:3, and 2 John 7 talk about this 'anti' christ. Simply put, someone who is against or opposed to or an opponent of or opposite of Christ. 1 John is the first place in scripture we read "antichrist", but as we noted above, earlier writers used different words to describe the same people, often quoting Jesus as he warned those of His day, and ultimately warns us today.
We have clear language definitions of who the antichrist is from the Apostle John. "Who is the liar? It is whoever denies that Jesus is the Christ. Such a person is the antichrist—denying the Father and the Son." (1 John 2:22) "...but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist..." (1 John 4:2) "I say this because many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the antichrist." (2 John 7)
It's urgently important we recall that everything done in the name of religion isn't approved by Christ, (Matt 7). With that in mind, we understand from 1 John 2:19 that many antichrists were at some point inter-mingled in the first century church. John says, "They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us." Only if we are blind would we think Satan would not infiltrate and deceive the church today in the same way, using people to teach false doctrine while deceptively rubbing elbows with us as one of us.
The point of all this is simply to remind us, we are surrounded by antichrists, and per the definitions John gave us there are perhaps millions or billions of them. Some have, do, and will probably stand out as head & shoulders above the rest, like Hitler, yet others who stand in opposition to our Lord are antichrist as well, and a few of them may even be in church assemblies on Sunday, perhaps even teaching and preaching. We don't like to think about that, but doesn't that fit the warnings of Christ that we quoted above?
That doesn't mean they are destined for hell, because the Gospel of Christ can change the hearts of mankind, and we pray it does. But it does mean we need to recognize them, otherwise we can't possibly heed the warnings we have in scripture regarding them, because according to scripture, their spirit is antichrist, they are lawless, and their doctrine is contradictory toward the word of God and they fail in recognition of Christ as the Son of God, and their contradictory doctrine is how we recognize them. Let us heed the warnings and be vigilant.