Ronald Jensen

Ronald Björn Jensen (April 1, 1936 – September 16, 2025) was an American mathematician who lived in Germany, primarily known for his work in mathematical logic and set theory. He completed a BA in economics at American University in 1959, and a Ph.D. in mathematics at the University of Bonn in 1964. His supervisor was Gisbert Hasenjaeger. Jensen taught at Rockefeller University, 1969–71, and the University of California, Berkeley, 1971–73. The balance of his academic career was spent in Europe at the University of Bonn, the University of Oslo, the University of Freiburg, the University of Oxford, and the Humboldt-Universität zu Berlin, from which he retired in 2001. He was honored by the Association for Symbolic Logic as the first Gödel Lecturer in 1990. In 2015, the European Set Theory Society awarded him and John R. Steel the Hausdorff Medal for their paper *K without the measurable*. Jensen died on September 16, 2025, at the age of 89. His notable results include work on Axiomatic set theory NFU, fine structure theory of the constructible universe L, infinitary combinatorial principles, Jensen's covering theorem for L, core models, consistency of the continuum hypothesis plus Suslin's hypothesis, and coding the universe by a real.