Benoit Mandelbrot passed away at the age of 85. He was best known for his work on fractals, a branch of mathematics with applications in biology, finance, physics, art and other areas involving roughness in growth processes in any complex system.
More: "A Theory of Roughness," an Edge lecture (via John Brockman)
Do I claim that everything that is not smooth is fractal? That fractals suffice to solve every problem of science? Not in the least. What I'm asserting very strongly is that, when some real thing is found to be un smooth, the next mathematical model to try is fractal or multi fractal. A complicated phenomenon need not be fractal, but finding that a phenomenon is "not even fractal" is bad news, because so far nobody has invested anywhere near my effort in identifying and creating new techniques valid beyond fractals. Since roughness is everywhere, fractals — although they do not apply to everything — are present everywhere. And very often the same techniques apply in areas that, by every other account except geometric structure, are separate.