Kari Hag

Kari Jorun Blakkisrud Hag was born on 4 April 1941 in Eidsvoll, Norway. She completed a cand.mag. at the Norwegian School of Education in Trondheim (Noregs Lærarhøgskule) in 1963, then a cand.real. at the University of Oslo in 1967. In 1968 to 1969 she worked as a research assistant to Professor Haakon Waadeland. She earned her Ph.D. in mathematics at the University of Michigan in Ann Arbor in 1972. Her dissertation, Quasiconformal Boundary Correspondences and Extremal Mappings, was supervised by Frederick Gehring.

In 1972 Hag joined the Norwegian Institute of Technology (NTH) in Trondheim as a lecturer in mathematics, later associate professor, and remained there as NTH became part of NTNU. She became a full professor of mathematics at NTNU in 2001, with particular responsibility for teacher education, and retired as professor emerita in 2011.

Her research was in complex analysis and geometric function theory, including quasicircles and quasiconformal mappings. With Frederick Gehring she co-authored The Ubiquitous Quasidisk (American Mathematical Society, 2012). At NTNU she belonged to the research group in complex and harmonic analysis.

She helped create the civil-engineering programme in industrial mathematics and later NTNU's science teacher (lektor) education. Her push for small-group teaching in core mathematics courses contributed to a sharp drop in failure rates and earned SINTEF's prize for outstanding pedagogical work in 1989. She served on the Rein committee on NTH studies (1982) and the Underdal committee (1995) that set terms for establishing NTNU. Campus initiatives linked to her include student workplaces in Nordre lavblokk and the restoration of guest researcher housing known as Kråkeslottet.

Hag was married for sixty years to the mathematician and colleague Per Hag, who died in 2023. She lived and worked for most of her adult life in Trondheim. Beyond research she was a long-standing advocate for gender equality in mathematics and for attracting girls to science. In 2000 NTNU gave her its gender equality award for that work. On 8 May 2025 she attended her own induction onto Trondheim's Wall of Feminism at Olavshallen, alongside other notable women in the city's history.

Kari Hag died in Trondheim on 15 April 2026, aged 85. Memorial tributes published in Universitetsavisa and Khrono in May 2026, signed by Anne Borg, Eivind Hiis Hauge, Kristian Seip and others, said failing health had marked her last years, especially after her husband's death in 2023. A specific medical cause of death was not publicly detailed in those tributes. Colleagues remembered her as a grand old lady who had long helped shape NTNU's development.

Hag is remembered as both a research mathematician in geometric function theory and a builder of Norwegian mathematical education and campus life. The Ubiquitous Quasidisk remains a reference for quasidisk theory. Industrial mathematics and science teacher education at NTNU, small-group pedagogy that cut failure rates, and physical campus facilities she championed continue her practical legacy. Her 2018 knighthood in the Order of St. Olav and her place on Trondheim's Wall of Feminism mark public recognition of a career spent opening mathematics to more students, especially women.