Rajbanshi ("dynasty of king"). According to the local myths, their ancestor Koch king Hajo established the kingdom of Kampur by the end of 15th century. There is also another legend concerning the ancestry of the Rajbanshis. When Parshuram had started destroying the Chhetria dynasty in India as his father's revenge, the Chhetri kings and their people escaped to save their lives. Ancestors of Rajbanshis themselves being Chhetries fled and started living in the forests of Nepal's Morang and Jhapa by hiding. In context of Nepal, King Prithvi Narayan Shah annexed the kingdom of the Rajbanshis into a unified Nepal state.
From the perspective of physical anthropology, the body structure of the Rajbanshis of Nepal looks like that of Mangol-Dravid people. Howerer, in complexion, they bear a resemblance to the Aryas.
The Rajbanshis call themselves the descendants of Suryabansi and revealtheir lineage (gotra) to be Kashyap. They follow Chhetri character and customs and add Singh and Rajbanshi to their names.The Koches call themselves the Rajput Chhetris. It is also said that Koch, Bhadai, Paliya, and Deshi including the Rajbanshi caste are the Dravidian castes of north-east and east Bengal. They are also thought to be the mixture of the Mongolian blood but they use Brahmins as priests in some of their religious rituals and follow the Hindu religion. There is no discrimination by status and level in their community. They can marry their co-lineage partners under the conditions of seven generations’ gap.
There are different kinds of Rajbanshis such as Koch Rajbabshi, Poundra Rajbabshi, Mech Rajbabshi, Newar Rajbanshi, Thakuri Rajbanshi and Khataha Rajbanshi. Like in Nepal, Ridge (1991), referring to Risely (1967), writes that there are also many types of sub-castes of the Koch Rajbanshisin the North Bengal, India such as Paliya, Sadhupaliya, Babupaliya, Deshi, Domasir, Modasi, Jaluwa, Tongriya, Khopriya, Gobriya, Kantai,Dhalai,Tiyar and Koch. These sub-castes of the Rajbabshis in India are not found in Nepal.
The first major king was Vishwa Singha, who established himself in 1515 as the ruler of the Kamata kingdom after the Khen dynasty was defeated by Alauddin Hussein Shah in 1498. According to J N Sarkar Viswa Singha belonged to one of the dominant Koch tribes, which were a collection of Mongoloid tribes. "Minjahuddin found the features of the Koch, Mech and Tharu tribes similar to a south Siberian tribe. Bryan Hodgson classes the Koches with the Bodo and Dhimal tribes. Buchanan agrees. Dalton takes them to be Dravidian. But Risley thinks they represented a fusion of Mongoloid and Dravidian stock, with the later predominating. According to Waddell Mongoloid type of Koches predominated in Assam." loosely allied to the Meches, Garos, Tharus and also Dravidians. They had adopted Hinduism a few generations before Vishwa Singha and claimed the Kshatriya varna. The earliest known ancestor of Viswa Singha was Haria Mandal, from the Chiknabari village in Goalpara district, the head of the twelve most powerful Koch families. He was married to Jira and Hira, daughters of a Koch chief named Hajo, after whom Koch Hajo was named. Viswa Singha was the son of Haria Mandal and Hira. But according to some Koch chronicles, a son of Haria Mandal, Chandan, became the king in 1510. Vishwa Singha, another son of Haria Mandal, became the king after Chandan.