Sabbatai Zevi was a 17th century Jewish mystic who proclaimed himself the Messiah. He gained many followers but later converted to Islam under threat of death. His movement, Sabbateanism, continued secretly. Jacob Frank claimed to be the reincarnation of Sabbatai Zevi and founded the Frankist sect in the 18th century, which incorporated non-Jewish, heretical beliefs and practices and was excommunicated from Judaism.