WHO is that? The best yet only way to identify her/him is to know from the Scriptures and the writings of the early Church Fathers what are her/his essential distinguishing features.
At the outset, let it be noted that Jesus never spoke of an Antichrist. He warned his disciples to beware of “false prophets” or “wolves in sheep’s clothing” but not of an Antichrist.
It was John who wrote of Antichrists (plural) in his two epistles as those who try to deceive the followers of Jesus just like the false prophets or wolves in disguise that Jesus spoke of. It is only in his Book of Revelations that he wrote of an arch Antichrist who will appear with terrible demonic powers just before the end of the world (or Christ’s second coming) to sow dissension among Jesus’s followers.
The world is not about to end (or is it?) and we have no idea when Christ’s second coming will take place. Hence we cannot be talking here of the Antichrist, the Devil incarnate, who will sow dissension among Jesus believers. We are only talking here of Antichrists today and before the end of the world.
And he or she is not an individual but a class of individuals, reminiscent and akin to the false prophets that Christ tells his disciples to be wary of. That is the first distinguishing feature.
The second is that Antichrists will deceive people into believing they are Christ or their message is from Christ. They cannot deceive if they appear like the devil. Wolves can only deceive if they come in sheep’s clothing as Jesus warned his disciples.
The demonic among us, therefore, and we do have these people, are not the Antichrists. If someone clearly thinks, speaks and acts like the Devil, she/he is not the Antichrist or false prophet John and Jesus spoke of. She/he is not deceiving believers because she/he is in wolf’s clothing and can easily be distinguished and shunned.
It is worth noting here that early Protestant Reformers have always considered the Pope as the antichrist for acting like God in claiming infallibility (Vatican I later in 1868-69 declared it a dogma) and making absolute laws for Christians to strictly follow that are not found in the Bible like, among others, the obligation of Sunday Mass or that priests should be celibate.
I am not saying the Protestant Reformers were right. I am not insinuating anything either. I am simply saying this is how they have interpreted, some of them until today, what the Bible and early Church Fathers say are the identifying features of Antichrists.
To sum up, except for the terribly Evil One who will come just before the end of the world to sow dissension among believers, today’s Antichrists are those that pretend to be Christ or from Christ but do not do His work.