Koch (caste)
Koch is a social group  in the Indian state of Assam. The members of the caste are converts from different ethnic groups such as the Bodos, Garos, Tiwas, Karbis, Ahoms, Hajongs, Chutias etc. The Koch is one of many categories in the tribe-caste continuum in Assamese society. In some instance, the identity of the Koch overlaps the identity of the Kachari. Any member of the any ethnic group can become a Koch by employing a Brahmin and giving up  habits such as the consumption of liquor, pork, beef etc. and giving up their original mother tongue which are considered to be impure in Hinduism. The caste is mostly found to be concentrated in Upper Assam section of the Brahmaputra Valley. See also
Boro people
Garo people
Tiwa (Lalung)
Karbi people
Assamese people

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Social groups of Assam 
Ethnic groups in South Asia
Ethnic groups in India
Indian castes