Elon Musk personally interviewed the first thousand SpaceX employees. Janitors, technicians, engineers. He has said that hiring is the part of building a company where mistakes are most expensive, and his own biggest mistake was weighting talent too heavily and personality not enough.
"The biggest mistake I've made is to put too much of a weighting on someone's talent and not enough on their personality. It actually matters whether somebody has a good heart."
His interview approach is deceptively simple. He asks every candidate the same thing: tell me the story of your life and the hardest problems you solved. Then he drills into the details. The people who truly did the work can go arbitrarily deep. They remember the specifics, the dead ends, the moments where things almost broke. People who exaggerated or rode someone else's contribution start repeating themselves or get vague.
"The people who really solved the problem know exactly how they solved it. They know the little details. Anyone who struggles hard with a problem never forgets it."
Musk does not care about degrees. He has publicly stated he does not care if someone graduated from high school. What he screens for instead is evidence of exceptional ability: open-source contributions, side projects, businesses started, hard problems solved. He wants to see "even one thing, but let's say three things, where you go: Wow." His four non-negotiable traits are a hardcore work ethic, talent for building things, common sense, and trustworthiness. Everything else, he says, is trainable.
"It is a mistake to hire huge numbers of people to get a complicated job done. Numbers will never compensate for talent in getting the right answer."
He has also learned to distrust impressive resumes. If the conversation does not match the paper, he trusts the conversation. Always. SpaceX runs seven to nine interview rounds, and a single strong objection from any interviewer can stop the process cold. There is no majority rules. The bar is the bar.