Political history of Sri Aurobindo
Anushilan Samiti was founded as an attempt to organize Bengali youth through a program of physical fitness and spiritual training for a nationalist program. By 1902, Calcutta had three societies working under the umbrella of Anushilan Samity, a society earlier founded by a Calcutta barrister by the name of Pramatha Mitra. These included Mitra's own group, another led by a Bengali lady by the name of Sarala Devi, and a third one led by Aurobindo Ghosh. The Anushilan Samiti had Aurobindo and Deshabandhu Chittaranjan Das as the vice-presidents, Suren Tagore the treasurer. Jatindra Nath Banerjee (Niralamba Swami), Bagha Jatin, Bhupendra Nath Datta (Swami Vivekananda's brother), Barindra Ghosh were among other initial leaders.
By 1905, the work of Aurobindo and his brother Barin Ghosh allowed Anushilan Samity to spread through Bengal.
Bagha Jatin
Several sources mention Jatin as being among the founders of the Anushilan Samiti in 1900, and as a pioneer in creating its branches in the districts. According to Daly's Report: "A secret meeting was held in Calcutta about the year 1900 [...] The meeting resolved to start secret societies with the object of assassinating officials and supporters of Government [...] One of the first to flourish was at Kushtea, in the Nadia district. This was organised by one Jotindra Nath Mukherjee ["sic"!].". Nixon reports further : "The earliest known attempts in Bengal to promote societies for political or semi-political ends are associated with the names of the late P. Mitter, Barrister-at-Law, Miss Saralabala Ghosal and a Japanese named Okakura. These activities commenced in Calcutta somewhere about the year 1900, and are said to have spread to many of the districts of Bengal and to have flourished particularly at Kushtia, where Jatindra Nath Mukharji ["sic"!] was leader." Bhavabhushan Mitra's written notes precise his presence along with Jatindra Nath during the first meeting. A branch of this organisation (Anushilan Samiti), was to be inaugurated in Dacca. In 1903, on meeting Sri Aurobindo at Yogendra Vidyabhushan's place, Jatin decides to collaborate with him and is said to have added to his programme the clause of winning over the Indian soldiers of the British regiments in favour of an insurrection. W. Sealy in his report on "Connections with Bihar and Orissa" notes that Jatin Mukherjee "a close confederate of Nani Gopal Sen Gupta of the Howrah Gang (...) worked directly under the orders of Aurobindo Ghosh."