The Origin of Bengali Brahmins

Ancient Bengal did not have any Brahmins in its community. It is popularly believed that Brahmins were brought in to preach Hindutva, though really not the Vedic Hinduism as it is commonly believed, but more of the Pouranik Hinduism type, which evolved after Buddhism flourished. This Pouranik Hinduism is what we know as Brahmanism .
It was circa 686 BC , when Bengalee society was under the direct influence of the Buddhists and the Jainis. The then king of Bengal, Aadishoor, son of Shashanka, started the procedure of luring Brahmins into the delta. King Shashanka never liked the Buddhists and Jainis, and his son followed in his father's way of thinking. Aadishoor is the first king of Bengal, who planned to spread Brahminism into the delta area to curb the increasing influences of the Buddhists and Jainis of that time.
It was he who took the initiative and brought in five families or group of families from the area called Brahambartya , specifically Kanauj and generally from the area between the Ganges and the Yamuna, which includes present day Haryana and a good chunk of Western Uttar Pradesh.
He brought in those five families or caste groups and helped them to settle down in five villages of the Rahr Bhoomi , i.e. the land south of the confluence of the Ganges and the Brahmaputra in Bengal. The five villages were :
Chatto
Mukhoti
Bandoghati
Gango
Ghoshan
The families which migrated became the pundits of the local villages under the auspicies and support of the King. These pundits were known as Upadhyays. From the names of the villages they worked in, these families got their titles over a period of time. These titles later on were adopted as the surnames of modern Bengalee Brahmins.
Thus the Upadhayay from Chatto village came to take on the title of Chattopadhyay and similarly the others came to be known as Mukhopadhyay, Bandopadhyay, Gangopadhyay and Ghoshal. These brahmins came to be known also as the Rahri Brahmins .
Barendra Bhumi , i.e. modern day North Bengal, similarly had its Brahminism awakening soon after the south got its share. Many years after Adishoor, Shyamal Varma, a Kshatriya King also brought five Brahmanas from Kanouj----
Sanaka; Bhardwaja; Savarna; Sandilya; Vasistha.
The Bhatariya,
Maitreya,
Satar,
Baghshree and
Laheria
villages soon gave birth to the Brahmin clans of Bhaduri, Moitra, Sanyal, Bagchi and Lahiri. These came to be known as the Barendra Brahmins .
Apart from the above two classes of Brahmins, there is another one called the Vedic Brahmins . They came in much later into the fold of the Bengalee society. They mainly dealt in performance of religious activities. These were the Bhattacharya and the Chakraborty. The Bhattacharyas became both the pujari and religious Gurus to the common people. The Chakrabortys restricted themselves to perform religious ritualistic activities only.