Estonian science has lost one of its great pioneers. On January 4th, mathematician and computer scientist Leo Võhandu (28.09.1929 – 4.01.2026), laureate of the Republic of Estonia Lifetime Achievement Award in Science, holder of the Order of the White Star, IV Class, and laureate of the Mente et Manu Medal of Merit, passed away.

Leo Võhandu was a trailblazer in the development of information technology and data analysis in Estonia. His scientific work spanned from computational mathematics and multidimensional data analysis to biomathematics and mathematical linguistics. Already in the 1960s, he created analytical solutions in which one can see the conceptual foundations of today's explainable artificial intelligence. His work was always centered on applying mathematical thinking to real, often very complex problems. "Mathematics has no content of its own, but mathematical models work everywhere and can be applied in every field," he said.

Leo Võhandu's scientific career was characterized by profound interdisciplinarity. He combined computer science and mathematical statistics with sociology, linguistics, medicine, and pedagogy, thereby making a significant contribution to the broadening of Estonia's scientific landscape. Under his supervision, 47 doctoral theses were defended, and many leading figures in Estonian science have emerged from among his students.

Leo Võhandu holds a special place in three Estonian universities. He graduated from the University of Tartu as a mathematician in 1952, where he developed as a scientist and lecturer. From 1966, he began working at Tallinn University of Technology, where he served as department head, vice dean, professor of fundamentals of informatics, and chair holder. From 1997, he was Professor Emeritus at Tallinn University of Technology, but actively participated in teaching and research until almost the end of his life in the former Institute of Informatics and current Institute of Software Science.

Leo Võhandu also made great contributions to launching and promoting informatics education at Tallinn University, where he also chaired the defense committee for informatics theses. Tallinn University named Leo Võhandu its Honorary Professor.

In the memories of colleagues and students, Leo Võhandu will live on as an exceptionally broad-minded scientist, visionary, and mentor, whose mathematical aptitude, phenomenal memory, and deep respect for other scientific fields left a lasting mark on Estonian science and education.

We express our condolences to his loved ones.

Leo Võhandu's funeral will take place on Monday, January 12th at 1:00 PM in the assembly hall of Tallinn University of Technology (Ehitajate tee 5). Please do not bring wreaths.

Tallinn University of Technology 
Tallinn University 
University of Tartu