Steve Jobs considered his signature style of black turtleneck and blue jeans to be a sort of personal uniform—which came to be because Apple employees rejected his idea for a company-wide uniform. Gawker has excerpts from the upcoming Steve Jobs biography by Walter Isaacson that explains the back story. It begins when Jobs, inspired by Sony, suggested that all workers wear a nylon vest made by designer Issey Miyake.
They rejected the idea ("Oh man, did I get booed off the stage"), but Jobs decided to adopt a personal uniform as a matter of convenience and style. "I asked Issey to make me some of his black turtlenecks that I liked, and he made me like a hundred of them," Jobs told Isaacson, before showing off stacks of them in his closet. "That's what I wear. I have enough to last for the rest of my life." Click to read how sales of similar turtlenecks rose after his death.