Biographer Walter Isaacson is shedding some light on the world of Elon Musk. 

The Tulane University professor, who shadowed the billionaire for two years, told CNBC on Monday that Musk has a "demon mode that is destructive." 

"That he wouldn't be who he is without both demon mode and his drive …," Isaacson explained, echoing remarks made on Twitter Spaces late last month. 

While the Tesla chief has demons and drives that motivate him, money is not number one, the writer explained. 

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"And, his management of Twitter has been because he really loves it, and he loves putting out impulsive tweets. And, he loves the contentiousness of it," Isaacson, a CNBC contributor, explained. 

What Musk does not have is a "fingertip feel" for empathy or emotions, Isaacson added, and said he was more impressed with the SpaceX founder as an engineer. 

Singer Grimes, Musk's ex-girlfriend, coined the term "demon mode," he said on Twitter Spaces. 

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Isaacson went into additional detail, saying Musk was nearly addicted to risk and a desire for drama and describing a "dark quality to his desire." 

One of these alleged triggers is when employees fail to match his "maniacal sense of urgency," which Isaacson said was one of his five principles. 

"I'd know that he was just going to rip the person apart," Isaacson recalled, saying the Twitter leader was just "brutal."

Requests for comment to Twitter and Musk went unaddressed at the time of publication. 

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That approach resulted in a "good" outcome 80% of the time, but reportedly – for the other 20% – it just made people afraid to give him bad news.

Isaacson's book is set to be released in September.