A false messiah is anyone who has falsely claimed to be the messiah. The Greek term pseudochristos was first used in the Synoptic Gospels. The later Hebrew term, possibly borrowed from the Greek, is mashiyah sheker (משיח שקר). The term pseudoprofetes, false prophet is much older, and found many times in the New Testament and in Josephus. The New Testament treats false messiahs, and antichrists as the synonyms. False prophets are a separate category.
The concept of an individual "false messiah" developed in medieval Christianity is absent from rabbinic literature. Only in the mid-seventh century does the Sefer Zerubbabel use the very rare term, mashiah sheker, false messiah. The Sefer Zerubbabel's Armilus is an anti-messiah figure in late-period Jewish eschatology, comparable to, and probably influenced by, the medieval Christian conception of a latter-day Antichrist and the Muslim Masih ad-Dajjal, who will conquer Jerusalem and persecute the Jews until his final defeat at the hands of God or the true Messiah. His inevitable destruction symbolizes the ultimate victory of good over evil in the Messianic Age or World to Come.
In the 7th century CE Sefer Zerubbabel, and 11th century Midrash Vayosha, this Armilus is "a king who will arise at the end of time against the Messiah, and will be conquered by him after having brought much distress upon Israel." The Jewish Encyclopedia (1911, 1964) entry continues "The origin of this Jewish Antichrist (as he can well be styled in view of his relation to the Messiah) is as much involved in doubt as the different phases of his development, and his relation to the Christian legend and doctrine."
Most mainstream Christians believe Jesus to be the Messiah, and regard any other past or future claimant as false. However Jesus himself warns of various "false messiahs". Matthew 24:4,6,24; Mark 13:5,21-22; and Luke 21:3 all use the term "pseudochristos" to refer to messianic pretenders.
al-Masih ad-Dajjal, Arabic for "the false messiah", is an evil figure in Islamic eschatology, directly comparable to the figures of the Antichrist in some forms of Christian eschatology and Armilus in Jewish eschatology, respectively. He is to appear, pretending to be Masih (i.e. the Messiah), at a time in the future before Yawm al-Qiyamah (Judgment Day).
- The Jewish Messiahs: From the Galilee to Crown Heights - Page 31 Harris Lenowitz - 2001 "During the Galilean rebellions, the term "false" was first applied to a prophet in a messianic context, paving the way for ... Matthew 24:4, 6, 24; Mark 13:5, 21-22; and Luke 21:3 all use the term pseudochristos to refer to messianic pretenders." ...the Greek term is borrowed and translated in the much later Hebrew term mashiah sheker, which reshapes and alters the previous Hebrew usage ...
- Redemption and resistance: the messianic hopes of Jews and ... - Page 294 William Horbury, Markus Bockmuehl, James Carleton Paget - 2007 "Indeed, the concept of a false prophet seems to be absent from rabbinic literature. And in the mid-seventh century, the Sefer Zerubbabel uses a very rare term, mashiah sheker, false Messiah"
- The Jewish encyclopedia 1964 Page 118 Isidore Singer, Cyrus Adler "ARMILUS: In later Jewish eschatology and legend, a king who will arise at the end of time against the Messiah, and will be conquered by him after having brought much distress upon Israel. The origin of this Jewish Antichrist (as he can well be styled in view of his relation to the Messiah) is as much involved in doubt as the different phases of his development, and his relation to the Christian legend and doctrine."
- Oxford Dictionary of World Religions, Al-Dajjāl, p. 43.