Nicolae Popescu (; 22 September 1937 – 29 July 2010) was a Romanian mathematician and professor at the University of Bucharest. He also held a research position at the Institute of Mathematics of the Romanian Academy, and was elected corresponding Member of the Romanian Academy in 1997. He is best known for his contributions to algebra and the theory of abelian categories. From 1964 to 2007 he collaborated with Pierre Gabriel on the characterization of abelian categories; their best-known result is the Gabriel–Popescu theorem, published in 1964. His areas of expertise were category theory, abelian categories with applications to rings and modules, adjoint functors, limits and colimits, the theory of sheaves, the theory of rings, fields and polynomials, and valuation theory. He also had interests and published in algebraic topology, algebraic geometry, commutative algebra, K-theory, class field theory, and algebraic function theory. Biography Popescu was born on September 22, 1937 in Strehaia-Comanda, Mehedinți County, Romania. In 1954 he graduated from the Carol I High School in Craiova and went on to study mathematics at the University of Iași. In his third year of studies he was expelled from the university, having been deemed "hostile to the regime" for remarking that "the achievements of American scientists are also worth of consideration." He then went back home to Strehaia, where he worked for a year in a collective farm, after which he was admitted in 1959 at the University of Bucharest, only to start anew as a freshman. Popescu earned his M.S. degree in mathematics in 1964, and his Ph.D. degree in mathematics in 1967, with thesis Krull–Remak–Schmidt Theorem and Theory of Decomposition written under the direction of . He was awarded a D. Phil. degree (Doctor Docent) in 1972, also by the University of Bucharest. While still a student, Popescu focused on category theory. He first approached the general theory, with its connections to homological algebra and algebraic topology, then shifted his focus on theory of Abelian categories, being one of the main promoters of this theory in Romania. He carried out mathematics studies at the Institute of Mathematics of the Romanian Academy in the Algebra research group, and also had international collaborations on three continents. He shared many moral, ethical, and religious values with Alexander Grothendieck, who visited the Faculty of Mathematics in Bucharest in 1968. Like Grothendieck, he had a long-standing interest in category theory and number theory, and