Elon Musk doesn't have a natural feel for empathy or emotions, says his biographer who's followed him for three years.

• Walter Isaacson commended Elon Musk's engineering abilities, but suggested he lacks empathy.

• Isaacson made the comments on CNBC's Squawk Box, discussing his upcoming biography of Musk.

• Musk's manner has drawn more scrutiny amid mass layoffs at Twitter and his anti-trans posts.

Walter Isaacson, whose upcoming biography about Elon Musk is expected in September, said one of his takeaways from three years of observing the voluble executive is that he may lack empathy.

"I'm more impressed with him as an engineer," Isaacson said in an interview on CNBC's Squawk Box, which tweeted a clip of the segment on Monday. "I think that he does not have a fingertip feel for, you know, empathy, emotions."

It's an idea that Isaacson has broached before. In an interview on Twitter Spaces last month, he made a reference to Musk's "demon mode," suggesting that the trait, while intimidating to employees, was part of Musk's success. He had credited the pop star Grimes, Musk's ex-girlfriend who has two children with him, for that vivid characterization.

He repeated the idea on CNBC's Squawk Box.

"The question when you write a biography though, is how do you take the dark threads and realize that you can't just pull them out?" Isaacson said on the segment. "That he wouldn't be who he is without both, demon mode, and his drive."

In the segment, Isaacson also addressed recent headlines about Musk, including a purported cage match with Meta CEO Mark Zuckerberg. Isaacson reiterated his view that chatter of a physical rumble was merely a "metaphor" for the two executives' business rivalry. Meta's Twitter rival Threads amassed some 100 million users in days after its launch this month.