Johannes Oecolampadius was a German Protestant reformer in the Calvinist tradition from the Electoral Palatinate. He was the leader of the Protestant faction in the Baden Disputation of 1526, and he was one of the founders of Protestant theology, engaging in disputes with Erasmus, Zwingli, Luther and Martin Bucer. Calvin adopted his view on the Eucharist dispute.
His German surname was Hussgen, which he etymologized to Hausschein and graecicized to Oecolampadius.