Hearing of the death of Benoit Mandelbrot sent me to the bookshelf to pick up The (Mis)Behaviour of Markets (which unfortunately seems to be out of print in the UK) and The Fractal Geometry of Nature (ditto). I can't quite remember when I first read about Mandelbrot's work and discovered the beauty of fractals. Not only does fractal geometry create beautiful images, it also seems obviously true as a mathematical description of nature. Certainly, Thomasina in Tom Stoppard's Arcadia thought so:

“If there is an equation for a curve like a bell, there must be an equation for one like a bluebell, and if a bluebell, why not a rose? Do we believe nature is written in numbers?”

I once interviewed Madelbrot for a BBC radio programme, and he had a wonderful phrase: “One hope for regularity but one lives in roughness.” The (Mis)Behaviour of Markets was published in 2004 and was prescient in its criticism of conventional financial economics and efficient markets theory in particular. (Naseem Taleb has long been a huge Mandelbrot fan.) Post-crisis, it repays rediscovery, although you might need to shop around to find a copy. Meanwhile, here is a video of John Authers of the FT interviewing Mandelbrot (aged 85 then) in 2009.