Benoit Mandelbrot died at the age of 85 today. Mandelbrot was the mathematician best known as the founder of fractal geometry. He was also a lifelong student of financial markets. His book, The (Mis)Behavior of Markets, was a classic that argued against the financial orthodoxy of building models based upon probabilistic risk assessments, and instead argued in favor of markets as being dominated by uncertainty (in a Knightian sense), turbulence, and non-linearities and being far more risky than standard models suggest. He will be missed.