Jewish adventurer whose grandiose plans inspired the messianic visions of the martyr Solomon Molcho (Molcho, Solomon) (q.v.; d. 1532). Reubeni claimed to be a prince descended from the tribe of Reuben (hence his name) of a Jewish state in Arabia. He gained the favour and protection of Pope Clement VII and King John III of Portugal with his forcefully stated plan to lead a Jewish army against the Turks in Palestine.

Under the influence of Reubeni's charismatic personality, a young Portuguese Marrano (a Jew forced to espouse Christianity), Solomon Molcho, openly adopted Judaism; his subsequent sermons inflamed the smoldering messianic hopes of many Jews. Reubeni rebuffed Molcho for his rashness; in turn, Reubeni aroused the displeasure of King John and was forced to leave Portugal.

Reubeni eventually went to Italy, only to find that Solomon Molcho had preceded him and was gaining a high reputation as an eloquent preacher of messianic visions. Joining forces, they left for Ratisbon (now Regensburg, Ger.), to see the Holy Roman emperor Charles V, who had convened Parliament there. The two visionaries tried to persuade Charles to arm the Jews to fight the Turks; instead, they were imprisoned, fettered, and sent to Mantua, Italy, to face the Inquisition. Molcho was burned at the stake, while Reubeni was sent to a Spanish prison, where he died a few years later, probably by poisoning.