An enduring food favorite of Elon Musk across 3 decades is Jack in the Box's teriyaki bowl

• Elon Musk frequently ate at Jack in the Box while working at his first startup in 1995, Musk's new biography revealed.
• Musk's favorite dish there was the teriyaki bowl, which he ordered again when he revisited the chain along with Walter Isaacson.

Elon Musk's workaholic tendencies date back to his first startup, Zip2, which he co-founded with his brother, Kimbal, in 1995. Zip2 was an online business directory with maps — which was eventually sold to AltaVista in 1999 for $307 million.

Back then, he would often sleep at the office and shower at the nearby YMCA and get angry at staff for not working past 9 p.m.

Musk's new biography, penned by Walter Isaacson and published Tuesday, sheds light on his favorite food while working at Zip2.

Elon and Kimbal mainly ate at the fast food chain Jack in the Box, which – according to Isaacson's retelling — was cheap, open 24 hours, and just a block away from their office.

"I can still tell you every single menu item," Kimbal told Isaacson, "It's just seared into my brain."

Elon's favorite dish? The San Diego, California, headquartered chain's teriyaki bowl, per Isaacson's book.

The biography also detailed Elon Musk's nostalgic visit to Zip2's former office 27 years after starting the company. When he couldn't get into the building, Musk visited the neighborhood Jack in the Box.

Musk told Isaacson, "I'm supposed to be fasting now, but I just have to get something here."

He ordered the teriyaki bowl for himself — and a hamburger for X, his son with Grimes. He told Isaacson, "I wonder if it will still be here twenty-five years from now so X can bring his kids here?"

Jack in the Box is a fast food chain founded in 1951. The West Coast fast food classic is known for its all-day breakfasts. In 2021, the company announced that it was acquiring Del Taco in a $575 million deal.

Musk isn't alone in loving fast food staples — Bill Gates and Warren Buffett are also self-declared fans of Coca-Cola. And Buffett even famously claimed to eat McDonald's and drink 5 cans of Coke daily, telling CNBC, "I always tell people: I found everything I like to eat by the time I was six."

Musk did not immediately respond to a request for comment from Insider, sent outside regular business hours.