He is spoken of as a real individual person and not an idea. The mystery of iniquity does exist, but this is not the Antichrist Paul says that will come. It is an Antichrist spirit. John says the same thing. John says there is an Antichrist person also.
Beast equals Antichrist.
He comes from the sea of people. He controls the ten member restored Roman Empire. Many people have found objects with that number. They are not a man. They could be spirits of antichrist.