As a high school student, Russell Johnson earned statewide acclaim in several subjects. After college, his career as a professor earned him international praise.

Johnson, who was born in Fairmont, Minn., focused on mathematics in college, earning a B.A. and Ph.D. from the University of Minnesota.

After the U, Johnson embarked on a long and prolific career as a professor of mathematics.

"Russell is an internationally known expert in dynamical systems — an area of mathematics which has many applications to other science and engineering disciplines," said Yingfei Yi, a math professor at the University of Alberta who worked on his Ph.D. under Johnson at the University of Southern California. "In particular, he is among early pioneers who made fundamental contributions to nonautonomous dynamics describing dynamical behaviors of time-dependent systems. He is widely regarded as a leader in that important subject."

During his academic career, Johnson authored or co-authored more than 140 articles and a book.

Johnson, who taught at the University of Florence, Italy, died on July 22 in Florence. He was 70.

"Russell was devoting, serious and a pure scholar," said Yi.

After earning his Ph.D. in 1975, Johnson started his academic career at the University of Wisconsin-Parkside. In 1976, he became an assistant professor at the University of Southern California. From 1981 to 1991 he was an associate or full professor at Southern California. In 1991, he moved to the University of Florence.

He returned to the University of Minnesota in 1980 and 1989-90 as a visiting professor. He also served as a visiting professor at the University of Heidelberg, Germany, from 1983-85. He also presented mini-courses at Peking University, the University of Valladolid, Spain, and East China Normal University.

During his graduate studies at the U, Johnson worked with Prof. George Sell. Sell, who passed away in 2015, and Yi co-wrote a biography of Johnson, which appeared in the September 2011 edition of the Journal of Dynamics and Differential Equations.

Sell and Yi wrote: "Russell has made extensive services to the international mathematical community. Besides being on numerous professional committees, he has organized more than twenty international conferences, workshops, and graduate summer schools.

"Russell is widely regarded as a world leader and pioneer in the dynamics of nonautonomous differential equations and skew-product flows. He has made widespread contributions, and his papers on topological dynamics and ergodic theory to differential equations are especially noteworthy."

Johnson attended Trimont High School. As a junior in 1964, Johnson won top honors in a World Affairs competition sponsored by the Minneapolis Star. During the summer between his junior and senior years, Johnson was one of a small group of students selected to attend a National Science Foundation program.

As a senior, he earned an "A" rating in the discussion division of the Region II speech contest. He also was one of 11,800 students from 230 schools statewide who took part in a contest sponsored by the Math Association of America and Society of Actuaries. Only 46 students (0.3 percent) earned a score of 50 or better. Johnson finished eighth.

Johnson is survived by his wife, Cristina Cafaro-Johnson; a daughter, Martina Johnson of Florence; mother Gladys Johnson of Trimont; brothers Keith of Omaha, Neb., and James of Lauderdale; sister Eileen Stoffels of Cedar; and nephew Karl Stoffels. Services have been held.

Joel Rippel • 612-673-4719