Martin David Kruskal (born 28.09.1925) is an American theoretical physicist and a member of the National Academy of Sciences. He was born in New York. He graduated from the University of Chicago (1945). In 1946-51 he worked at New York University. Since 1951 he has worked at the plasma physics laboratory of Princeton University (professor from 1961).
His research was in the field of mathematical physics, applied mathematics, magnetohydrodynamics, plasma physics and controlled thermonuclear fusion (the stability of a plasma, the theory of solitons, the theory of adiabatic invariants). Together with M. Schwarzschild he predicted (1954) the instability of a plasma with a sharp boundary held by a magnetic field (the Kruskal–Schwarzschild instability). Independently of V. D. Shafranov he obtained the criterion for the helical instability which determines the choice of the main parameters of toroidal thermonuclear devices of the Tokamak type (the Shafranov–Kruskal criterion). He studied (1957) the propagation of nonlinear steady plasma waves. Together with others he laid the foundations of a new method of solving nonlinear partial differential equations, the method of the inverse scattering problem (1967). In 1960, independently of G. Szekeres, he constructed the system of coordinates that covers the Schwarzschild geometry most completely. He introduced the concept of solitons in a plasma.