Answer
Bhaktisiddhanta Sarasvati took initiation into Gaudiya Vaishnavism in 1900, when he was 18 years old. His guru was Bhaktivinoda Thakura, who had been a disciple of the great Bengali poet and religious reformer Chaitanya Mahaprabhu. Sarasvati was a prolific writer and scholar, and he played a major role in reviving the Gaudiya Vaishnava tradition in the early 20th century.