New biographical data about the Russian scientist-geologist, specialist in the field of petrography B. V. Zalessky are identified and specified. The links in the history of the Zalessky (Zalesky) family, which belonged to the hereditary nobility of the Kazan province, who had estates in the Vyatka, Kazan and Kostroma provinces, are being restored. Verified information about the closest relatives of B. V. Zalessky is provided: his great-grandfather — the honorary caretaker of the Yaransky district school P.A. Zalessky; grandfather — a member of the city council of Kazan, comrade of the mayor and acting mayor N. P. Zalessky; father — the prosecutor of the Vyatka, then the Kazan district court, later the assistant to the chief prosecutor of the Criminal Cassation Department of the Government Senate V. N. Zalessky (erroneously presented in the works of a number of researchers as “Zalsky”), etc. The characteristic of the personality, scientific activity and social circle of B. V. Zalessky is given. His relations with famous figures of Russian science and culture — M. M. Bakhtin, the Florensky family are considered. Scattered information contained in various sources — unpublished (archival) and published (scientific articles and monographs, memoirs and epistolary sources, documentary prose, reference and encyclopedic literature and Internet publications) is collected and generalized.