Ancient history.
"For many deceivers have gone out into the world, those who do not acknowledge Jesus Christ as coming in the flesh. This is the deceiver and the antichrist." 2 John 1:7
"and every spirit that does not confess Jesus is not from God; this is the spirit of the antichrist, of which you have heard that it is coming, and now it is already in the world. " 1 John 4:3
"Children, it is the last hour; and just as you heard that antichrist is coming, even now many antichrists have appeared; from this we know that it is the last hour." 1 John 2:18
John is the only writer of the New Testament to employ the term "antichrist" in speaking of those, or that which is, opposed to Christ.
From all these passages, how can we say that any one is the antichrist and deny that all the others are? If one opposes Christ, you are against, anti.
Adam Clarke in commenting on I John 2:18 says this about the antichrist: "Any person, thing, doctrine, system of religion, polity, etc., which is opposed to Christ, and to the spirit and spread of his Gospel, is antichrist . . . Every man who opposes the spirit of the Gospel, and every teacher and writer who endeavors to lower the Gospel standard to the spirit and taste of the world, is a genuine antichrist, no matter where or among whom he is found." (Vol. VI, p. 909).
John said there are "many.' Then it does not refer to a single person as such. He said the antichrist was already in the world. He said the one who denies that Christ came in the flesh is A deceiver and AN antichrist, so it would refer to any whose attitude and actions deceive and who are against the teachings of the Christ.
