Sigurdur Helgason *54

At the age of 96, Sigurdur died Dec. 3, 2023, in Belmont, Mass.

He was born in Akureyri, Iceland, in 1927. Enthralled with mathematics from birth, as a child he enjoyed measuring circular objects around his home to calculate pi.

After beginning at the University of Iceland, he studied mathematics at the University of Copenhagen. In 1952, he came to Princeton on a Fulbright grant and earned a Ph.D. in mathematics in 1954.

Following positions at MIT, Princeton, the University of Chicago, and Columbia, he joined the MIT faculty and remained for more than 60 years. Sigurdur’s contributions to mathematics include the texts Differential Geometry and Symmetric Spaces, and Differential Geometry, Lie Groups, and Symmetric Spaces. His research contributions include the Plancherel and Paley-Wiener theorems for Riemannian symmetric spaces, and he helped create the modern theory of Radon transforms.

Sigurdur held honorary doctorates from the University of Copenhagen, the University of Iceland, and Uppsala University, and was awarded the American Mathematical Society’s Steele Prize. On his 80th birthday, in Reykjavik he chaired an international conference on integral geometry, harmonic analysis and representation theory.

Sigurdur is survived by his wife of 66 years, Artie; children Thor and Anna; and four grandchildren.

Graduate alumni memorials are prepared by the APGA.