History records that a Portuguese Marano, Diego Peres (born 1500), after being spurned by Jewish adventurist David Reuveni, circumcised himself, changed his name to Shlomo Molcho, and went on a mission to convince Maranos everywhere to return to Judaism. History records, also, that he correctly predicted a flood in Rome and an earthquake in Portugal, gaining him the respect and protection from the Inquisition from Pope Clement VII. He later fled to Turkey and Eretz Israel and was known to be a student of Rabbi Joseph Karo, among others. In 1532 he was burned at the stake by Emperor Charles V of the Holy Roman Empire. See, e.g. Dimont, Max I., "Jews, God and History." Secular historians have named Molcho as a false messiah. Yet in some Hasidic circles -- especially those of Galicia and Hungary -- he is revered as a saint and Kabbalist. Which version is true?
R' Chaim Vital writes that he used "Practical Kabbalah" inappropriately, and there is a tradition that one who uses it inappropriately (like if one is ritually impure from a corpse) will either get sick (he or his descendant) or he (or his descendant) will convert out. He says that Rabbi Shlomo Molcho (emphasis mine) was an example of one who used "Practical Kabbalah" and was uprooted from the world.
However, the Lubavitcher Rebbe said that he was a great Mekubal, he had Mesirus Nefesh to debate with the Pope, and he wanted to bring the Geula. He failed, but merited giving his life Al Kiddush Hashem (which is something the Beis Yosef wanted his whole life).