Elon Musk's office sleeping habits have existed since the early 1990s, according to a book about his first startup

• Elon Musk founded his first startup, Zip2, with his brother in 1995.
• Jimmy Soni's "The Founders" details how he slept at the office and openly berated colleagues.
• Nearly three decades later, the billionaire is managing Twitter with the same intensity.

Elon Musk's management of Twitter has become notorious for long hours and strenuous demands on staff, but before he was a billionaire, Musk behaved similarly at his first startup, according to "The Founders" by Jimmy Soni.