Wikipedia
Maitra alternatively spelled Moitra is a Bengali Hindu family name found among the Bengali Brahmins of the Kulin Varendra clan.
It is one of the oldest surnames of Bengal, coming from the Varendra Brahmin clans.
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 . Varendra (Barendra) Bhumi, i.e. modern-day North Bengal, had its Brahminism awakening soon after the south got its share. Shyamal Varma, a Kshatriya King brought five Brahmanas from Kannauj - Sanaka, Bhardwaja, Savarna, Sandilya, and Vasistha.
The Bhatariya, Maitreya, Satar, Baghshree, and Laheria villages soon gave birth to the Bengali Brahmin clans with surnames like Bhaduri, Moitra/Maitra, Sanyal, Bagchi, and Lahiri/ Lairi. They came to be known as the Kulin Varendra (Barendra) Brahmins of Bengal, and are regarded as the highest Hindu caste in Bengal along with the Kayasthas and Baidyas.
"Debotar Grash" a famous poem by RabindraNath Tagore, pays tribute to the heroism of one aged Maitra Brahmin who sacrifices his life to save a small child during a pilgrimage journey through a tumultuous Bay of Bengal.
"Maitra" can also refer to a Buddhist philosophy, from its roots in the Sanskrit word "Maitreya".