Prior to boarding the missing Titanic submersible, British billionaire Hamish Harding had previous experience with high-stakes journeys.

The 58-year-old, who works in the business aviation industry, has embarked on explorations that have taken him from the deepest parts of the ocean to beyond the highest points in the sky, according to Action Aviation, an international aircraft brokerage company of which Harding is Chairman.

Harding's past expeditions include the One More Orbit project, a record-breaking 46-hour circumnavigation of Earth by plane, and a trip to space last June with Blue Origin's New Shepard rocket as one of six passengers. Blue Origin is an aerospace company founded by Amazon's Jeff Bezos that offers flights to space, which have sold in the past for upwards of $28 million, per the company's website.

Harding also witnessed the reintroduction of Cheetahs from Namibia to India and conducted several South Pole visits, Action Aviation wrote in a statement posted to social media on June 20.

His latest trip to view the wreckage of the RMS Titanic—the passenger liner that infamously sank in 1912 and inspired James Cameron's 1997 Titanic—wasn't his first time partaking in a deep dive. He previously boarded a submersible to the Challenger Deep—the deepest point of the ocean—in the Mariana Trench, according to Action Aviation.

Harding's explorations have earned him a Guinness World Record for longest duration at full ocean depth by a crewed vessel for his venture into the Mariana Trench located East of the Philippines, according to online records.

The businessman is one of five passengers being rescued in an international mission before oxygen on the 21-foot submersible—named Titan—runs out. The trip was offered by company OceanGate Expeditions, which sells tickets for $250,000, according to NBC News.

Harding was aboard to conduct research, according to Richard Garriott, who is president of The Explorers Club, a scientific exploration group that counts Harding as a member.

"When I saw Hamish last week at the Global Exploration Summit, his excitement about this expedition was palpable," Garriott wrote in a statement for The Explorers Club posted June 29. "I know he was looking forward to conducting to research at the site."

In a follow-up statement, Garriott confirmed that fellow Explorers Club member Paul-Henri Nargeolet was also among the missing passengers and expressed that the organization has been rallying "far and wide" to provide support in the rescue mission.

"We have much greater confidence that: 1) There is cause for hope, based on data from the field—we understand that likely signs of life have been detected at the site; 2) They precisely understand the experienced personnel and tech we can help deploy," Garriott wrote on June 20. "3) We believe they are doing everything possible with all resources they have; and 4) We now have direct lines to the highest levels of Congress, The Coast Guard, Air Forces, Navy and The White House, thanks to your support."

Keep scrolling to learn more about the five passengers aboard the missing Titan submersible, which went missing on June 18 an hour and 45 minutes into its dive.

On June 18, 2023, a deep-sea submersible Titan, operated by the U.S.-based company OceanGate Expeditions and carrying five people on a voyage to the wreck of the Titanic, was declared missing. Following a five-day search, the U.S. Coast Guard announced at a June 22 press conference that the vessel suffered a "catastrophic implosion" that killed all five passengers on board.

Pakistani-born businessman Shahzada Dawood and his 19-year-old son Suleman Dawood, both British citizens, were also among the victims.

Their family is one of the wealthiest in Pakistan, with Shahzada Dawood serving as the vice chairman of Engro Corporation, per The New York Times. His son was studying at the University of Strathclyde in Glasgow, Scotland.

Shahzada's sister Azmeh Dawood told NBC News that Suleman had expressed reluctance about going on the voyage, informing a relative that he "wasn't very up for it" and felt "terrified" about the trip to explore the wreckage of the Titanic, but ultimately went to please his father, a Titanic fan, for Father's Day.

The Dawood Foundation mourned their deaths in a statement to the website, saying, "It is with profound grief that we announce the passing of Shahzada and Suleman Dawood. Our beloved sons were aboard OceanGagte's Titan submersible that perished underwater. Please continue to keep the departed souls and our family in your prayers during this difficult period of mourning."

OceanGate CEO Stockton Rush was the pilot of the Titan. The entrepreneur—who founded the research company in 2009 in Everett, Wash.—had long been interested in exploration. Rush, 61, previously said he dreamed of becoming the first person on Mars and once said that he'd "like to be remembered as an innovator."

In addition to leading voyages to see the remnants of the Titanic, Rush had another surprising connection to the historic 1912 event: His wife Wendy Rush is the great-great-granddaughter of a couple who died on the Titanic, Ida and Isidor Straus.

British billionaire Hamish Harding confirmed he was a part of the mission in a June 17 Instagram post, a day before the submersible went into the water and disappeared.

"I am proud to finally announce that I joined @oceangateexped for their RMS TITANIC Mission as a mission specialist on the sub going down to the Titanic," he wrote. "Due to the worst winter in Newfoundland in 40 years, this mission is likely to be the first and only manned mission to the Titanic in 2023. A weather window has just opened up and we are going to attempt a dive tomorrow."

Harding—the chairman of aircraft company Action Aviation—said the group had started steaming from St. Johns, Newfoundland, Canada and was planning to start dive operations around 4 a.m. on June 18. The 58-year-old added, "Until then we have a lot of preparations and briefings to do."

His past explorations included traveling to the deepest part of the ocean in the Mariana Trench, telling Gulf News in 2021, "It was an incredibly hostile environment. To travel to parts of the Challenger Deep where no human had ever been before was truly remarkable."

The Dubai-based businessman also circumnavigated the Earth by plane with the One More Orbit project and, last year, took a trip to space on Amazon founder Jeff Bezos' Blue Origin New Shepard rocket. Harding shared his love for adventure with his son Giles, described as a "teen explorer" on his Instagram.

As for the fifth member, a representative for French explorer Paul-Henri Nargeolet told the New York Times that he was a passenger on the Titan, with Harding also referencing him on Instagram as a member of the team. 

The Times described him as a maritime expert who was previously part of the French Navy. The 71-year-old was a bonafide Titanic specialist and has traveled to the wreckage 35 times before. Nargeolet served as the director of RMS Titanic, Inc., a company that researches, salvages and displays artifacts from the famed ship, per the outlet. 

Alongside fellow passenger Hamish Harding, he was a member of The Explorers Club, founded in 1904.

As Harding noted in his post, the submersible—named Titan—was a part of an OceanGate Expeditions tour that explores the wreckage of the RMS Titanic, which infamously sank in 1912.

The company expressed its sympathies to the families of the victims. "These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world's oceans," OceanGate said in a statement. "Our hearts are with these five souls and every member of their families during this tragic time. We grieve the loss of life and joy they brought to everyone they knew."