Walter Isaacson talked to the New York Times about his planned biography of Elon Musk, the controversial SpaceX and Tesla CEO.

Isaacson, known for his biographies including Benjamin Franklin and Steve Jobs, has spoken to 200 people about the South African–born businessman, he said.

“It wasn’t like I pursued him or he pursued me,” Isaacson told the Times. “We started talking about it, seeing if it would make sense. I have no deal with him, there’s no contract, it was just, ‘Will you give me access? And he said, ‘I’ll do it,’ and I said, ‘Yeah, I think I’ll do it.’ Ten minutes later, he tweeted it out.”

Musk’s tweet, posted last August, wasn’t directly confirmed by Isaacson at the time. Musk has since announced that he plans to buy Twitter, although the deal has yet to be approved by government regulators.

Isaacson said it was challenging to keep tabs on Musk’s quickly changing life.

“Dealing with his life is like trying to take notes while drinking from a fire hose,” he said. “It keeps coming fast.”

“It is definitely going to be a challenge,” he added. “This thing really is a movable feast. But the main thing is just to make it a clear narrative, from a troubled childhood in South Africa to becoming one of the most influential people on the planet.”

Michael Schaub, a journalist and regular contributor to NPR, lives near Austin, Texas.