Tosio Kato, whose career in mathematics ranged over more than 40 years, made major contributions to the field of mathematical physics. A prolific writer, he produced hundreds of published articles during his career. His most important research, on perturbation theory, won him acclaim and awards in both his native country of Japan and in the United States, where he spent most of his career.

Kato was born on August 25, 1917, in Tochigiken, Japan, the son of Shoji and Shin (Sakamoto) Kato. He attended the University of Tokyo, where he received a bachelor's degree in 1941; he would receive a doctor of science degree from the university ten years later. In 1943, he began teaching at the University of Tokyo, and due to the stability this position provided he was able to marry Mizue Suzuki the following year.

Even before his appointment to full professorship at the university, which he achieved upon receiving...