San Marco Fractal
The San Marco Fractal is a Julia set which uses the most common formula z = z^2 + c. In the San Marco Fractal, c = -1, or -1 + 0i. When Benoit Mandelbrot found this fractal, its shape reminded him of the San Marco Cathedral whose reflection can be seen in the flooded streets of Venice. That is the only reason why this fractal became more famous than the other Julia Sets.
Notice that is the fractal we used for the background of our logo in the top-left corner of the page.