Alexander Petrovich Kotelnikov, an outstanding Russian mathematician and mechanic, was one of the founders of non-Euclidean mechanics and the geometry of space-time. His works had a significant impact on the development of geometry and theoretical mechanics. Son of a colleague of the great Lobachevsky P. and . Kotelnikova, a student of major Kazan mathematicians F. M. Suvorov and A. In. Vasilyeva, who did much to develop and spread Lobachevsky's ideas, Alexander Petrovich Kotelnikov was a teacher of many Soviet mathematicians and mechanics, personifying a living connection between Lobachevsky and our Soviet science. The book about the life and activities of a talented scientist is of great interest to the reader interested in the development of Russian and Soviet science.