Leo Jud (also Leo Juda, Leo Judä, Leo Judas, Leonis Judae, Ionnes Iuda, Leo Keller) (1482 – 19 June 1542), known to his contemporaries as Meister Leu, Swiss reformer, was born in Guémar, Alsace.
He was educated at Basel, where after a course in medicine he turned to the study of theology. This change was due to the influence of Huldrych Zwingli, whose colleague at Zürich Jud became after serving for four years (1518–1522) as pastor of Einsiedeln.
His assertion that Martin Luther with Zwingli about the Eucharist prompted Luther to publish several sermons on the subject in his 1526 The Sacrament of the Body and Blood of Christ—Against the Fanatics.
His chief activity was as a translator; he was the leading spirit in the translation of the Zürich Bible and also made a Latin version of the Old Testament.