As one of the richest men in the world, John Walton (search) could have spent his entire life traveling around the globe on luxury jets. But the heir to the Wal-Mart fortune loved to tool around Wyoming in a cheap airplane built from a kit.

Walton died Monday at the age of 58 when the homemade experimental plane he was piloting crashed near the Jackson airport in Grand Teton National Park (search).

Walton was remembered as a humble man with a passion for education, the outdoors and all things flying.

"He was the kind of guy you'd never imagine had 20 billion," said Michael Collins, a flight instructor at Jackson Hole Aviation. "He didn't put on airs, you know what I mean? He could have just been one of the guys."

Walton's father was Sam Walton (search), who founded the discount store chain that would later become one of the biggest companies in the world. In March, Forbes magazine listed John Walton as No. 11 on the list of the world's richest people with a net worth of $18.2 billion. He was tied with his younger brother, Jim — one spot behind his older brother, Rob, who is Wal-Mart chairman.

John Walton was on a company committee that reviews Wal-Mart finances and oversees long-range planning but was not widely regarded as being a potential successor to his brother. Acquaintances described him as one who preferred to avoid publicity.

The cause of the crash was under investigation. The National Transportation Safety Board said Walton was flying a CGS Hawk Arrow (search), a kit-built plane priced from about $9,000 up. It was not known whether Walton built the plane himself.

Joan Alzelmo, spokeswoman for Grand Teton National Park, said the NTSB informed park officials Tuesday it would take over the investigation.

"There's a lot of national attention being paid to this," said Alzelmo said. "It happened in a national park to a person known nationally. I think everyone wants to make sure no stone is unturned."

Walton served in Vietnam, where he was a Green Beret medic and volunteered for a covert operation behind enemy lines. He won the Silver Star for saving the lives of his team members when they were under fire on a reconnaissance mission in Vietnam.

He opted against joining the family business after coming home from the war, saying it was too confining, according to a Forbes magazine interview last year. He attended company shareholder gatherings, but generally limited his appearances to a wave to the crowd while his older brother conducted the meetings.

In 1998, he and Ted Forstmann founded the Children's Scholarship Fund to provide tuition assistance for low-income families wanting to send their kids to private schools. The fund has benefited 67,000 students.

Friends said Walton also chaperoned regular ski outings for kids at a local ski resort and volunteered at his son's school.

Despite his fortune, "he had no ego in this game, which is why he was so revered," said Dan Peters, chairman of the Philanthropy Roundtable, of which Walton was a part.

One of Walton's biggest hobbies was flying, and he was a frequent face at the airport in Jackson. He also built boats and his own motorcycle and worked as a crop duster in the 1970s. The crash happened while a Cessna business jet he used sat on a runway near his Wyoming home.

John S. Meyer, who was in the special forces with Walton, recalled how decades ago they used to talk over a game of poker, a favorite pastime of Walton's, about what they would do when the war was over.

"'When I get out of here, when I survive this,"' Meyer remembered his friend saying, "'I'm going to go home and get a motorcycle. I'm going to get my pilot's license. I want to see the country.' And he did."