for the remainder of his career, and supervised seven doctoral students. During the writing of his last book, Theory of group representations, Naimark was too sick to write by himself, and so completed it by dictation to his wife. Naimark died on 30 December 1978 at age 69 after a prolonged illness, and was buried in Kuntsevo Cemetery in Moscow. He had written 123 papers and five books. Work Naimark's interests were formed in the 1930s during a golden age of functional analysis in the USSR. His early work with Krein included development of the theory of separation of roots of algebraic equations. Naimark also began to take interest in pedagogical techniques at this time, an interest that stayed with him for the rest of his life. After moving to the Steklov Institute of Mathematics for his D.Sc. Naimark worked intensively on spectral theory, extensions of symmetric operators, and the representation theory of locally compact operators. His collaboration with Israel Gelfand in the 1930s and 1940s led to several fundamental results in functional analysis, including the 1943 Gelfand–Naimark theorem and the GNS theorem. During his service in World War II Naimark wrote several papers on seismology, and helping to develop the Spectral theory of ordinary differential equations. He worked especially on second-order singular differential operators with a continuous spectrum, using eigenfunctions to describe their spectral decompositions, and studying the concept of a spectral singularity. His results are summarized in the monograph Linear Differential Operators, which was published in 1954. In 1956 Naimark published his monograph Normed Rings, which gave the first comprehensive treatment of Banach algebras, and was enormously influential in the development of the field. His 1958 monograph Linear representations of the Lorentz group helped to develop the theory of representations of the fundamental series of the complex classical groups, beginning with SL(2,C). With Zhelobenko he later generalized these results to all complex semisimple Lie groups. In the 1960s Naimark's interests focused more intensively on the representation theory of groups and algebras in spaces with an indefinite metric, which became the subject of his last (1976) monograph, The theory of group representations. Naimark's name is associated with several important ideas in functional analysis: The Gelfand–Naimark theorem on the representation of C*-algebras by bounded operators Naimark's dilation theorem on extensions of symmetric operators The Gelfand–Naimark–Segal construction (the GNS construction) establishing a correspondence between cyclic *-representations and linear functionals Naimark's problem