The Adi Dharma Brahmic religion was originated by the Bengali Brahmin Thakur clan of Ram Mohan Roy, Dwarkanath Tagore and Prasanna Coomar Tagore who were Rarhi Brahmins of the Vandhopadyaya (Sandilya gotra) division.
This Adi Brahma religion Adi Dharma was originally propounded by these highest caste Kulin Brahmins of Bengal who were excommunicated from Hindu faith for opposing social and priestly evils of the time (18th and 19th century AD). Previously the original ancestors (5 legendary Brahmin scholars of Kannauj Kanyakubja school deputed to the King of Bengal) of all these Highest caste twice born Bengali Brahmins had been excommunicated from Kannauj (Central Provinces) in 10th/11th cent. AD after their return from Bengal.
"Mobility" ie. leaving the home and being exposed to external influence meant loss of caste for Brahmins (a social device to conserve meagre land holdings and priestly incomes).
Mobile scholars of priestly Brahmin clans such as these in contact with (or in the service of) foreign rulers - like the Mughals or European Companies or Indian princelings - were deliberately ostracised by their "fixed" priestly Hindu clan peers (relatives) ensconced within the numerous temples of Bengal and denied their shares of ancestral undivided properties and incomes. As a consequence ghastly social evils like Sati (or the burning alive of Hindu widows) were encouraged, primarily by the fixed priestly class. The mobile clan members banded into associations (Sabhas) to oppose these unBrahmic practices colliding head on with orthodox ("fixed") Hindu society in Bengal.
The Mughal 'Raja' Rammohun was the first Indian to cross the seas to Britain in 1833, followed by 'Prince' Dwarkanath in 1842. Refusing to recant and knowing that so strong was the prejudice against them at home, both opted to die and be buried there.