Rescue crews are on day four searching for the missing submersible vessel near the Titanic wreckage. Among the five people inside the vessel is Stockton Rush. He’s the CEO of the company leading the expedition. He's also a Princeton university alum. His passengers are a British adventurer, two members of a Pakistani business family and a Titanic expert.

On Wednesday morning, the US Coast Guard said a Canadian aircraft successfully detected underwater noises. The search teams are now relocating. Ships, planes and even an underwater robot have been deployed.

There is less than a day of oxygen left in the vessel.

MORE: Coast Guard bringing in new ships, underwater vessels to search for lost sub near Titanic

Although his background is in aerospace and technology, Rush founded OceanGate Inc. in 2009 to provide crewed submersibles for undersea researchers and explorers, according to the company's website. Rush is the Titan's pilot, said company spokesperson Andrew Von Kerens.

The private company based in Washington started bringing tourists to the Titanic in 2021 as part of its effort to chronicle the slow deterioration of the wreck.

“The ocean is taking this thing, and we need to document it before it all disappears or becomes unrecognizable,” Rush told The Associated Press in 2021.

In an interview with CBS News last year, Rush defended the safety of his submersible but said nothing is without risk.

“What I worry about most are things that will stop me from being able to get to the surface — overhangs, fish nets, entanglement hazard,." he said, adding that a good pilot can avoid such perils.

Rush became the youngest jet transport rated pilot in the world at age 19 in 1981, and flew commercial jets in college, according to his company biography. He joined the McDonnell Douglas Corp. in 1984 as a flight test engineer. Over the past 20 years, he has overseen the development of multiple successful IP ventures.

Greg Stone, a longtime ocean scientist and a friend of Rush, called him “a real pioneer” in the innovation of submersibles.

“Stockton was a risk-taker. He was smart. He was, he had a vision, he wanted to push things forward,” Stone said Tuesday.