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.

Donald Trump and Elon Musk are spending a lot of time around each other these days. How strong is their friendship?

The White House is trying to calm concerns about the future of Social Security amid Elon Musk's latest comments and critics warning the Trump administration is 'gutting it.'