Baron Wilhelm Emmanuel von Ketteler (25 December 1811 – 13 July 1877) was a German theologian and politician who served as Bishop of Mainz.

[2] In 1851, he founded the congregation of the Sisters of Divine Providence, with Stephanie Amelia Starkenfels de la Roche.

[citation needed] He is cited in Pope Benedict's encyclical Deus caritas est for his role in the Catholic social tradition.

In 1861, Ketteler published a book on reconciliation between Catholics and Protestants in Germany, Freiheit, Autorität, und Kirche; in it, he proposed the founding of a prayer society "for the Reunion of Christendom".

[3] Ketteler was friends with Julie von Massow, a Lutheran woman from Prussian nobility, who established one of these prayer societies.