Jonathan died in his sleep in a New Jersey hospital on January 16, 2020, at the age of 77.
Born in New York City in 1943, Jonathan was a brilliant mathematician who taught hundreds of university students, spoke at many math conferences, and published dozens of math papers even in his final years.
Jonathan received his B.A. with honors from the University of Wisconsin in 1962. He got his Ph.D. in mathematics from Princeton University in 1965 at the age of 22. He went on to teach math for many years at The Courant Institute at NYU, CUNY, Rice University, and Yeshiva University.
Jonathan loved playing chess, listening to jazz, swimming, watching tennis, and traveling to France and Japan.
Jonathan is survived by his wife Hisayo Foster, brother Michael Sondow, sons James Sondow and Joe Sondow, and two granddaughters.