Koch Hajo (1581-1616) was the kingdom under Raghudev and his son Parikshit Narayan of the Koch dynasty that stretched from Sankosh river in the west to the Bhareli river in the east on the north bank of the Brahmaputra river. It was created by dividing the Kamata kingdom then under Nara Narayan in medieval Assam. The Sankosh river divided the two new kingdoms, and it is roughly the boundary between the present-day Assam and West Bengal. The western half of the Kamata kingdom emerged as Koch Bihar whereas the eastern half emerged as Koch Hajo. The name Hajo comes from the legendary king Hajo, a Koch tribal chief and an ancestor of the Koch dynasty, who ruled over the Rangpur division in present-day Bangladesh and some regions of present-day Assam.