Martin David Kruskal, one of the world's pre-eminent applied mathematicians and mathematical physicists, died on December 26, 2006, at the age of 81. He was the recipient of many honors during his lifetime, including the National Medal of Science awarded by President Clinton in 1993, the 2006 Steele Prize for Seminal Contribution to Research and the Gibbs Lectureship, both from the American Mathematical Society, the Dannie Heineman Prize from the American Physical Society, and the Maxwell Prize from the International Congress on Industrial and Applied Mathematics. He was awarded memberships in the National Academy of Sciences, the American Academy of Arts and Sciences, and foreign memberships in the Royal Society of London, the Royal Society of Edinburgh, and the Russian Academy of Natural Sciences.

Professor Kruskal worked at Princeton University from 1951-1989, where he initially joined the Princeton Plasma Physics Laboratory, and was a member of both the Astrophysics and Mathematics Departments. At Princeton, he was also the founding director of the Program in Applied and Computational Mathematics. In 1989, upon becoming emeritus at Princeton, he joined the Mathematics Department at Rutgers University, where he held the David Hilbert Chair of Mathematics.

After receiving his undergraduate degree from the University of Chicago, Professor Kruskal received his Ph.D. under Richard Courant at New York University in 1952. He started his career at the Princeton Plasma Physics Laboratory with Project Matterhorn, then a classified project, to produce controlled thermonuclear fusion. In the 1950's, he made a number of seminal contributions including Kruskal-Shafranov Instability, Bernstein-Greene-Kruskal (BGK) Modes, and MHD Energy Principle, which laid the theoretical foundations of controlled nuclear fusion and the then undeveloped field of plasma physics. In 1960, he developed the well-known Kruskal Coordinates (also called Kruskal-Szekeres Coordinates), used in the theory of relativity to explain black holes.

He is most famous for his role in starting the "soliton revolution," considered one of the great mathematical advances of the last half of the twentieth century. In an astonishing discovery, he and Norman Zabusky found nonlinear waves that behave in many ways like linear waves, which they termed "solitons." Solitons are now known to be ubiquitous in nature, from physics to chemistry to biology. Their unique properties make them useful for communications, such as in undersea, fiber optic cables. They have even been seriously suggested as the basis for computing (soliton computers).

Professor Kruskal and his colleagues also devised an ingenious method to solve the equations underlying solitons, later called the Inverse Scattering Transform (IST), which has had a profound influence on both pure and applied mathematics. Until that time, nonlinear partial differential equations were thought to be essentially unsolvable.

Professor Kruskal's passion for research was legendary. Colleagues who worked with him understood that his day often began in the afternoon and ended when most people were having breakfast. Almost invariably, his research did not end with the proof, but continued until the subject was clarified to his complete satisfaction.

In later years, Professor Kruskal devoted himself to the study of surreal numbers, while continuing to work on nonlinear partial differential equations. He is also known among magicians for his invention of a card trick called the "Kruskal Count." Over the years, Professor Kruskal mentored generations of young mathematicians, and he continued teaching and publishing until the end of his life.

Professor Kruskal came from a family of mathematical siblings. His older brother, William Kruskal, was a statistician, best known to the public for the Kruskal-Wallis test, which is part of every major statistical computation system. His younger brother, Joseph Kruskal, is well known for Kruskal's Algorithm in computer science, the Kruskal Tree Theorem on well-quasi-orderings, and the formulation of Multidimensional Scaling.

Martin Kruskal is survived by his wife of 56 years, Laura Kruskal; three children, Karen, Kerry and Clyde; and five grandchildren.