Money isn't Elon Musk's number 1 motivator, says biographer who trailed him for 3 years

• Walter Isaacson said on CNBC's Squawk Box that Musk's biggest motivator doesn't appear to be money.
• He shared his view that Musk's love of "contentiousness" is behind his decision-making with Twitter.

For the world's richest person, Elon Musk is not all about the money.

That's according to Walter Isaacson, the biographer who spent three years trailing Musk for a book releasing in September.

"There are a lot of weird things and demons and drives that motivate him, but money isn't number one," Isaacson said in a recent CNBC Squawk Box interview which was posted on Monday.

"I think that if he wanted to make money, he wouldn't have bought Twitter. He wouldn't have sent rockets to Mars, and he probably wouldn't do electric vehicles," he added.

Despite sweeping changes at Twitter since a $44 billion acquisition in October, Musk announced on Saturday that the company was still losing money due to declining ad revenues, Insider reported.

In a conversation about the declining ad revenues, Isaacson did not explicitly state what Musk's primary motivation is but said he thought Musk's penchant for being a contrarian drives his decision-making at Twitter. "He loves putting out impulsive tweets, and he loves the contentiousness of it. His favorite line in a movie is: "Are you not entertained?" — that final line of 'The Gladiator.'"

Musk is no stranger to contentiousness, having drawn both plaudits and criticism for his management style.

Isaacson's upcoming Musk biography is expected to delve into his "abrupt Jekyll-and-Hyde mood swings" and a "craving for drama," according to book publisher Simon & Schuster.

The biographer has also previously made references to Musk's "demon mode" — describing him as industrious but "dark" and "with a real lack of empathy." Insider's Sarah Jackson previously reported that Musk's approach to management often involves "nano-management" and explosive rage-firings.

Despite Twitter's ongoing struggles, Musk's wealth continues to grow. Last month, Musk once again regained the title of the world's richest person, with a current net worth of $254 billion, per the Bloomberg Billionaires Index. This was largely due to a surge in Tesla's share price, Insider reported.

His spacecraft startup, SpaceX, is now worth nearly $150 billion, making it the most valuable startup in the US, Insider's Joseph Wilkins reported last week.

Isaacson did not immediately respond to Insider's request for comment outside of regular business hours.