Jeff Bezos said in a video posted to Instagram that he’s wanted to go to space his whole life, and that he asked his brother to come along “because we’re closest friends”. 

So who is the younger Bezos? Here are five things we know about him.

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Mark Bezos is the youngest of the Bezos siblings

According to a 1999 Wired profile on Jeff Bezos, Mark Bezos is six years younger than his brother, who turned 57 in January. The brothers have a middle sister named Christina. 

The Bezos siblings moved around a lot as kids, spending time in Albuquerque, Houston and Pensacola, Florida. Their mother, Jackie, had Jeff as a teenager; their father, Mike, immigrated to the US from Cuba at age 15. The couple met while working at a local bank, and Mike Bezos became Jeff Bezos’ adoptive father. 

He got his start in advertising and marketing

Mark Bezos attended Texas Christian University, graduating in 1992 with a degree in advertising and public relations, according to his LinkedIn page.

He got his start working at New York City ad firms like DDB and Saatchi & Saatchi. Then, in 1999, he founded and ran his own marketing company. The same year, he became a director at the Bezos Family Foundation, which was founded by Jackie and Mike Bezos.

In 2006, he began working at an organisation called Robin Hood, not to be confused with the stock-trading app – Robin Hood is a New York-based non-profit focused on fighting poverty. Bezos currently serves on Robin Hood’s leadership council.

Bezos is also the co-founder of private equity firm High Post Capital.

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He’s a volunteer firefighter

Bezos has been a volunteer with the Scarsdale Fire Department in Westchester County since 2005.

In 2011, he gave a Ted talk about being a firefighter, sharing a humorous story about being asked to do the unglamorous job of retrieving shoes for a woman whose house was on fire. But after hearing the woman’s appreciation, he said, he saw the importance of committing small acts of kindness and generosity. 

“I would offer this reminder: don’t wait,” Bezos said. “Don’t wait until you make your first million to make a difference in somebody’s life.” 

He’s likely a millionaire several times over

Jeff Bezos’ parents invested US$246,000 in Amazon in 1995, and while they haven’t publicly disclosed their Amazon holdings since 1999, they likely own millions of shares worth tens of billions of dollars, according to Bloomberg.

Mark and Christina also own shares in Amazon and are most likely worth several hundred million dollars apiece.

Last month, Mark put his Scarsdale home on the market for US$11 million. The 1.6-hectare (four-acre) estate includes a main house with six bedrooms and four bathrooms, as well as a four-bedroom guest house. The property also includes a home theatre, gym, wine cellar and game room with a golf simulator.

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Mark and his brother Jeff are close friends

In a Seattle Times profile on Jeff Bezos from 1999, Mark described what it feels like when your brother starts becoming famous. 

Mark interviewed Jeff onstage at a Summit leadership event in 2017 and joked about his brother’s astronomical wealth. 

“If any of you do get confused, I’m the one with the smaller bank account to your left,” Mark said.

For his part, Jeff has described his brother as the “funniest guy in my life” and said that when they’re together – often drinking bourbon – “I just laugh continuously.” 

The two brothers also support each other. According to the Seattle Times story, Jeff showed up at Mark’s first marathon in New York and started jogging with him at 40km (mile 25) to offer moral support, ducking out right before the finish line. 

In the video about the upcoming space flight, Mark said he was “awestruck” that Jeff asked him to come. 

“What a remarkable opportunity, not only to have this adventure, but to be able to do it with my best friend,” Mark Bezos said.

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This article originally appeared on Business Insider