Sabbateans
Donmeh is a Turkish word for a religious convert. It refers to a group of Jews of the Near East who followed Sabbatai Zevi (Shabbatai Zvi) and converted to Islam in 1666. Zevi's conversion is generally understood to have been forced.
While outwardly Muslim, the Donmeh secretly remained Jews, and continued to practice Jewish rituals covertly. They worshipped Sabbatai Zevi as the Messiah and an incarnation of God, observe certain Jewish rituals and pray in Hebrew and Aramaic and secretly celebrate Jewish festivals and fasts. They also observe rituals celebrating Zevi.
Some of the original Donmeh were Muslims who were converted to Sabbtianism.
There were several branches of the Donmeh. The first was the Ismirli formed in Izmir in what is now Turkey. The second were the Jakubi founded by a successor to Zevi who also made messianic claims. Also were the Othman Baba led by Berechia. This group taught Jacob Frank who led the Frankists in 18th century eastern Europe and the fifth were the Lechli who are of Polish descent who lived in exile in Salinika and Constantinople.
As of 2000, there were an estimated 15,000-50,000 members of the Donmeh, mostly in the cities of Adrianople, Istanbul, Salonika, and Smyrna, in the Near East.
See also: converso.