Bhaktisiddhanta Sarasvati (Bhaktisiddhanta Sarasvati; Bengali: bhktisiddhaant srsbtii; Bengali: [bhoktisiddhanto SoroSboti] ( listen); 6 February 1874 - 1 January 1937), born Bimala Prasad Datta (Bimala Prasad Datta, Bengali: [bimola proSad dotto]), also referred to as Bhaktisiddhanta Sarasvati Thakura, was a prominent guru and spiritual reformer of Gaudiya Vaishnavism in the early 20th century in India. Bimala Prasad was born in 1874 in Puri (Orissa) a son of Kedarnath Datta Bhaktivinoda Thakur, a recognised Bengali Gaudiya Vaishnava philosopher and teacher. Bimala Prasad received both Western and traditional Indian education and gradually established himself as a leading intellectual among the bhadralok (Western-educated and often Hindu Bengali residents of colonial Calcutta), earning the title Siddhanta Sarasvati ("the pinnacle of wisdom"). Under the direction of his father and spiritual preceptor, Bimala Prasad took initiation (diksha) into Gaudiya Vaishnavism from the Vaishnava ascetic Gaurakishora Dasa Babaji, receiving the name Shri Varshabhanavi-devi-dayita Dasa (Sri Varsabhanavi-devi-dayita Dasa, "servant of Krishna, the beloved of Radha"), and dedicated himself to arduous ascetic discipline, recitation of the Hare Krishna mantra on beads (japa), and study of classical Vaishnava literature.

The encounter with and initiation from Gaurakishora Dasa Babaji, an illiterate yet highly respected personality, had a transformational effect on Siddhanta Sarasvati. Later, reflecting on his first meeting with the guru, Bhaktisiddhanta Sarasvati recalled:  It was by providential dispensation that I was able fully to understand the language and practical side of devotion after I had met the practicing master [Gaura Kishora Das Babaji]....No education could have prepared me for the good fortune of understanding my master's attitude....Before I met him my impression was that the writings of the devotional school could not be fully realised in a practical life in this world. My study of my master, and then the study of the books, along with the explanations by Thakura Bhaktivinoda [Bhaktisiddhanta's father Kedarnatha Datta], gave me ample facility to advance toward true spiritual life. Before I met my master, I had not written anything about real religion. Up to that time, my idea of religion was confined to books and to a strict ethical life, but that sort of life was found imperfect unless I came in touch with the practical side of things.  After receiving initiation, Siddhanta Sarasvati went on a pilgrimage of India's holy places. He first stayed for a year in Jagannath Puri, and in 1904 travelled to South India, where he explored various branches of Hinduism, in particular the ancient and vibrant Vaishnava Shri and Madhva sampradayas, collecting materials for a new Vaishnava encyclopaedia. He finally settled in Mayapur 130 km north of Calcutta, where Bhaktivinoda had acquired a plot of land at the place at which, according to his research, Chaitanya Mahaprabhu was born in 1486. At that time, Bhaktivinoda added the prefix "bhakti" (meaning "devotion") to Siddhanta Sarasvati, acknowledging his proficiency in Vaishnava studies.  Starting from 1905, Bhaktisiddhanta Sarasvati began to deliver public discourses on the philosophy and practice of Chaitanya Vaishnavism, gathering a following of educated young Bengalis, some of whom became his students. While assisting Bhaktivinoda in his developing project in Mayapur, Bhaktisiddhanta vowed to recite one billion names of Radha (Hara) and Krishna - which took nearly ten years to complete - thus committing himself to the lifelong practice of meditation on the Hare Krishna mantra taught to him first by his father and then by his guru. The aural meditation on Krishna's names done either individually (japa) or collectively (kirtana) became a pivotal theme in Bhaktisiddhanta's teachings and personal practice.

How did he live a spiritual life?
After receiving initiation, Siddhanta Sarasvati went on a pilgrimage of India's holy places.