Who is the liar, if it is not the one who denies that Jesus is the Christ? This is the antichrist, who denies the Father and the Son.
The liar and antichrist is the one who denies that Jesus is the Christ and so denies Father and Son.
This verse states the central doctrinal mark of antichrist.
18Children, it is the last hour; and just as you have heard that the antichrist is coming, so now many antichrists have appeared. This is how we know it is the last hour. 19They went out from us, but they did not belong to us. For if they had belonged to us, they would have remained with us. But their departure made it clear that none of them belonged to us. 20You, however, have an anointing from the Holy One, and all of you know the truth. 21I have not written to you because you lack knowledge of the truth, but because you have it, and because no lie comes from the truth. 22Who is the liar, if it is not the one who denies that Jesus is the Christ? This is the antichrist, who denies the Father and the Son. 23Whoever denies the Son does not have the Father, but whoever confesses the Son has the Father as well.