Marhwini (‘Friend of Horses’) was a prince of Rhovanion during the time of the invasion of the Wainriders (19th Century TA). Following the death of his father, Marhari, and the defeat of the Northmen by Easterlings in the Battle of the Plains, he led a remnant of his people up the Anduin and into the forest vales; these refugees became the origin of the Éothéod. Those who could not or did not escape became the subjects of the victorious Wainriders.
Marhwini took part in the uprising of the enslaved northfolk and led a cavalry charge which finally overthrew the Easterlings and drove them back into the east. The former lands of Rhovanion remained in dispute, and Marhwini was forced to abandon them and remain instead by the Anduin.