This cuts to the heart of the futurist vs fulfilled debate.

1 John 2:18 says:

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.

John wasn't pointing ahead to a future, singular antichrist. He was warning his readers that what they had heard about was already happening. The word "antichrist" is never used in Revelation, Daniel, or Paul's letters. It's only in John's epistles, and every time it's used, it's plural or describing a spirit or character, not a specific future world ruler.

John defines antichrists as:

"They went out from us..." (1 John 2:19) – apostate Jews or false teachers

"Who is the liar but the one who denies that Jesus is the Christ? This is the antichrist..." (1 John 2:22)

"...every spirit that does not confess Jesus is not from God; this is the spirit of the antichrist..." (1 John 4:3)

There is no hint that John was expecting one final evil man far in the future. He said plainly, "Even now many antichrists have appeared", and "This is how we know it is the last hour."

So the idea of one future Antichrist doesn't come from John at all, it was added later through misunderstanding and misapplication of prophetic texts.

John's warning was urgent, for his audience, in his time, and his message was: the Antichrist spirit is already here.