Mr. Musk is fundamentally a creature of Silicon Valley, a scene that initiated an entire revolution in power dressing. The young masters of that universe dressed down to show that they were members of a new elite — one that refused to dress like the grown-ups they were about to topple. It was the defeat of the suit by the T-shirt.

Elon Musk, wearing his standard uniform of a black sport coat over a black T-shirt, was seen shaking hands and waving to other attendees. He was with a woman wearing a floor length gown who appeared to be Shivon Zilis,