The Dimasa people (or Dima-fisa, and also called Dimasa-Kachari) are a group of people in Assam, in northeastern India Dimasa mythology says they are the children of Bangla Raja and the great divine bird Arikhidima. Bangla Raja's six sons—Sibrai, Doo Raja, Naikhu Raja, Waa Raja, Gunyung Brai Yung, and Hamyadao—and Arikhidima are their ancestors, and in Dimasa belief, are ancestral gods. They are called Madai in Dimasa. Evil spirits born of the seven eggs of Arikhidima are responsible for disease, suffering and natural calamities. Dimasa is short for Aarikhidimasa-Khidima-Dimasa. The Dimasa lived along river banks and coasts in and near Kachar (Kachari) . After the Raja Ashoke period, a Dimasa leader named Bodo introduce the Budhist religion. Bodo Kachari is the offspring of Bodo Raja.

Ancient Dimasa tradition maintains that sixty thousand moons (Lunar months) ago, they left their ancestral land when it suffered a severe drought. After a long wandering, they settled at Di-laobra Sangibra, the confluence of the Brahmaputra and Sangi or Di-tsang. There they held a great assembly. The place is near the present Sadiya of upper Assam, where the Kacharis established their first Seat. Over time, their kingdom over large territories.