Rumengan is the divine lord and deified ancestor (opo') of Mount Mahawu, the volcano that faces Mount Lokon across the valley of Tomohon in the Tombulu country of Minahasa; the mountain itself was also called Mount Rumengan after him. In the Tombulu genealogy recorded at the Kakaskasen spring sites he is the elder son of Muntu-untu and Rumintu'unan and a grandchild of Toar and Lumimuut. He married a woman named Kati, known as Katiwiey, and settled about Mahawu; when his younger brother Pinontoan of Lokon carried her off and renamed her Katiambilingan, the brothers fought at the place afterwards called Pinahwela'an, 'the place of struggle', at the foot of Lokon, each hurling the ash of his own volcano against the other. They were at last reconciled at a spring thereafter named Kaimeye, 'the one to whom people come', where they swore to live in peace and fixed a hunting boundary between their domains, promising that no eruption of Lokon or Mahawu would cast its material beyond the agreed line. On Mahawu a rock dwelling is still remembered in local tradition as the house of Opo' Rumengan and was resorted to by ritual specialists.