The Department of Mathematics at Illinois Urbana-Champaign is sad to announce that Professor Emeritus Zhong-Jin Ruan has passed peacefully on September 20, 2025, at Carle Hospital. Zhong-Jin had a long and impactful career here at Illinois. From the obituary, “His doctoral research produced a landmark result in operator spaces, recognized with the Alfred P. Sloan Doctoral Dissertation Fellowship. In 1988, he joined the University of Illinois at Urbana-Champaign, where he spent more than 30 years teaching, mentoring, and conducting research. He published extensively, co-authored the influential book Operator Spaces, and received the Mahlon M. Day Award for Distinguished Mathematical Research. He also served as editor for leading mathematics journals and organized international conferences.”
Zhong-Jin will be remembered fondly by his colleagues and collaborators with Professor Renming Song stating, “Zhong-Jin was the ultimate gentlemen. He was quiet but he was always ready to help when needed. He helped me quite a bit when I first arrived at UIUC.” By all accounts, Zhong-Jin will be remembered as a kind man with a passion for mathematics.
Professor Emeritus Florin Boca also commented on Zhong-Jin’s enduring legacy, “Zhong-Jin Ruan made major contributions to the study of Operator Spaces and of Noncommutative Harmonic Analysis. The elegant groundbreaking abstract characterization of Operator Spaces from his Ph.D. thesis paved the way for subsequent spectacular developments in the area. The results achieved by Zhong-Jin and other prominent mathematicians (Effros, Blecher, Paulsen, Junge, Haagerup, Pisier, Kirchberg, Ozawa, Vaes, among others) projected Operator Spaces as ubiquitous objects of interest in several areas of Functional Analysis.
“Zhong-Jin served on the editorial board of Illinois Journal of Mathematics, Journal of Mathematical Analysis and Applications, and other mathematical journals. As one of the main organizers of the Wabash Seminar in Modern Analysis for more than two decades, until shortly before his retirement, he relentlessly promoted high quality research and supported talented mathematicians at the beginning of their careers. Zhong-Jin will be fondly remembered for his integrity, generosity and kindness. He will be missed dearly.”
In lieu of flowers, the family has asked that people donate to the Zhong-Jin Ruan Memorial Scholarship in Mathematics Fund at the University of Illinois Foundation which will be used to support future mathematicians at Illinois.