Musk’s occasional girlfriend — Claire Boucher, a musician known by her professional name Grimes — described the moments when Musk grows increasingly angry as his “demon mode,” Isaacson said.

“He has many personalities, and sometimes you’re around a really, you know, half-joking guy or a guy playing, you know, engineering mode, in which he’s really good. But there’s times he goes into what Claire Boucher, his occasional girlfriend known as Grimes, calls, “demon mode,” and that’s when he gets dark,” Isaacson said.

Isaacson noted that Musk has not been officially diagnosed but sometimes “talks about bipolar” to describe his symptoms. He also had been on a wide range of prescription medications, Isaacson said.

“He hasn’t been officially diagnosed, he says, but he talks about bipolar. He takes a lot of prescription medicines at times. He can be variable in his moods, and sometimes has a Jekyll and Hyde quality, where he will go into a dark, depressed mood and say some things, sometimes things that his father said to him, and then a few hours later, you ask him about it. And it’s like he almost has no memory.”

Musk has symptoms consistent with Dissociative identity disorder [DSM-5 300.14] previously known as multiple personality disorder, a mental health condition where a person experiences two or more distinct identities or personality states. It is often associated with severe childhood trauma and is characterized by memory gaps between these different identities.