What it's like to work with a billionaire, according to ex-colleagues of Elon Musk, Jeff Bezos, Bill Gates, and Sara Blakely

• The lives and working routines of billionaires fascinate those who want to understand their success.

• Past colleagues discussed working with Bill Gates, Elon Musk, Jeff Bezos, and Sara Blakely.

• They shared lessons they'd learned from the four well-known billionaires.

The lives and working routines of billionaires fascinate those hungry to understand their success. Their eccentricities and rules for life are the subject of books, podcasts, and countless articles.

Their close colleagues know these captivating figures well. Here, people who've worked alongside Elon Musk, Jeff Bezos, Bill Gates, and Sara Blakely talk about what it was like.

Bill Gates could tell when someone had 'slung the bull'

Chris Williams will never forget the "grilling" he says the billionaire Microsoft cofounder Gates gave him when they first met in 1992.

After buying their company, Gates interrogated Williams and his colleagues about why their product was better than its Microsoft rival's. In eight years of meeting regularly one-on-one with Gates as a Microsoft executive, Williams learned how Gates' questioning was a way of exposing who "slung the bull." He'd keep pressing until the person under questioning would either admit they didn't know or start inventing things.

"It was hard to be in those rooms many times and not pick up some of that skill," Williams wrote for Insider, adding: "In time I could recognize the face of someone who, it seemed, would rather die than say, 'I don't know, but I'll find out and get back to you.'"

Williams also recalled Gates' ability to absorb "miles of data and dozens of opinions on the correct path" at a meeting and immediately identify what mattered and what to do.

Read more: I worked closely with Bill Gates for 8 years as an executive at Microsoft. Here are the 3 lessons he taught me that I'll never forget.

Jeff Bezos insisted on a 'deliberately inefficient' meeting

Colin Bryar, a former Amazon vice president and chief of staff to Bezos, listed 13 insights he gained in the 12 years of working closely with him.