Rulman Merswin (around 1307 - 1382) was a German mystic, leader for a time of the Friends of God.
He was originally a successful merchant in Strasbourg. In 1347, he retired from business to join the Friends of God as one of mystic Johannes Tauler's disciples.
In 1367, he purchased an old cloister on an island near Strasbourg, and called it "das grüne Wört" ("the green island"). The house served as a refuge for study for the Friends of God. In 1371, it was put under the care of the Knights of St. John.
Merswin is generally considered the author of many writings attributed to the "Friend of God from the Oberland."