(portrait of the Antichrist, from Francis Barrett's The Magus, 1801)
The Antichrist (from the Greek antichristos: adversary of Christ) is mentioned in the Bible in the First and Second Epistles of John, where the term is applied to anyone who in the "last time" (see I John 2:18) denies that Jesus is the Christ, that is to say, the Anointed One.
The Antichrist came to be viewed as a single spiritual being who would oppose Jesus at the apocalypse due to the following verse (I John 4:3):"And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God; and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already it is in the world."
There is no explicit mention of the Antichrist in Revelation, but it is not uncommon to find the second Beast who is mentioned in Revelation 13:11-8 referred to as the Antichrist. The magician Aleister Crowley believed himself to be the first Beast foretold by St. John, and seems to have thought that his magical child would be the second Beast and the Antichrist, who would realize Crowley's vision of the Aeon of Horus in fire and blood -- a prophecy that some believe is presently unfolding as the Age of Aquarius dawns.
The second Beast has the two horns of a lamb and speaks with the voice of a dragon. He is able to use the power of the first Beast to draw fire down from the heaven and to perform wonders, so that "the earth and them which dwell therein" worship the first Beast and erect an image to the first Beast. By the agency of the second Beast, the image of the first Beast is given life. The image then puts to death everyone who will not worship it, and causes a mysterious mark to be inscribed on every person's right hand or forehead. This mark is usually understood to be the number 666. However, in Revelation three identifiers of the first Beast are mentioned: his mark, his name, and the number of his name (see Revelation 13:17).
In medieval legend the Antichrist is to be born from a sexual union between a virgin girl and a demon. This was the belief of St. Jerome. The magician Merlin was fabled to have been born into the world in this manner, and destined to become the Antichrist, but his destiny was supposedly changed when a priest baptized him as an infant. Other Fathers of the Church, such as St. Ireneus, St. Ambrose and St. Augustine, held that the Antichrist would be a mortal man born in the ordinary way, but more wicked than other men, a kind of demon incarnate.
From certain biblical hints it was widely believed in past centuries that the Antichrist would be a Jew of the tribe of Dan -- a superstition that no doubt served to further inflame anti-Semitic feelings in Europe. This belief was based on the remark of Jacob on his deathbed to his sons, "Dan shall be a serpent by the way, an adder in the path, that biteth the horse heels so that his rider shall fall backward" (Genesis 49:17). Also used as evidence for this belief was the exclusion in Revelation 7:5-8 of the tribe of Dan from the enumeration of the tribes sealed in the forehead with the seal of God.
(Antichrist by Lucas Cranach the Elder, from The Nuremberg Chronicle, 1493)