One of the Northmen who had allied themselves with Gondor in the middle years of the Third Age, and dwelt in the wide plains of Rhovanion south and east of Mirkwood. Marhari was a leader of these people in the time when the warlike Wainriders emerged out of the east, and with Narmacil II of Gondor he rode to meet them in battle. The resulting Battle of the Plains was a disaster for Gondor and its allies: Narmacil was killed, and Marhari fell in his rearguard.
Marhari's son Marhwini led a body of the surviving Northmen away from the now dangerous lands of Rhovanion, and travelled up the Vales of Anduin into the north. Through these travellers, and across many centuries, Marhari would become a distant ancestor to the people known as the Rohirrim.