Elon Musk, the SpaceX founder, Tesla CEO, and richest person in the world, is writing a book about his experiences running his two massively successful companies, Business Insider reports.

Musk made the announcement, obliquely, in a series of tweets on Saturday. “Time to tell the story of Tesla and SpaceX. Of Earth and Mars. Of lessons learned.”

“Are you writing a book?” asked a Twitter user, to which Musk replied, “Yes.”

Musk founded SpaceX, an aerospace manufacturer, in 2002. Two years later, he became chairman of the board of electric car company Tesla; he became CEO in 2008.

He’s courted controversy for some of his incendiary tweets, including one last March in which he wrote, “The coronavirus panic is dumb.” In November, he tested positive for Covid-19. Musk has also gained attention for his eccentric personal life. His partner is the musician Grimes; they named their first child “X ÆA-XII.”

News of Musk’s planned book might come as a surprise to some of his admirers. One month ago, responding to a tweet by author Ben Mezrich, Musk tweeted, “I am primarily trying to advance two causes: sustainable energy and extending life/consciousness beyond Earth. There is also the existential threat of AI, which we should aspire to mitigate. This doesn’t leave time to write books.”

Michael Schaub is a Texas-based journalist and regular contributor to NPR.