In late January 1991, billionaire David Koch showed up for a midweek date at a private club on the East Side of Manhattan. He was headed to meet Julia Flesher, a charmer from Little Rock, Arkansas, who was an assistant to the dress designer Adolfo and who had been introduced to Koch by mutual friends.

The two hit it off, but they didn’t have time for another rendezvous because he was due to fly to Ohio the next day for a series of meetings, then on to Los Angeles, where another meeting (and another date with a different woman) awaited.

On February 1, he boarded USAir Flight 1493 in Columbus, scheduled to arrive in L.A. at 6:11 p.m. Koch was in an aisle seat in the second row in first class, across from an elderly couple. The flight was uneventful, but immediately after the plane touched down at LAX, about a third of the way down the runway, Koch felt a violent shudder and heard the sickening sound of crunching metal. A shower of sparks passed the window to his left. A ball of fire rolled by.  A flight attendant came on the plane’s P.A. system, yelling, “Stay down! Stay down! Stay down!”

The pilot had failed to see a SkyWest Metroliner commuter plane carrying 12 passengers and crew members. Air-traffic controllers had cleared it to taxi into the path of the USAir 737, which was now crushing it under Koch’s feet.

The jet took a violent left turn as the wreckage of the commuter plane became wedged in the plane’s left landing wheel. The 737 charged across the taxiway at high speed. “I stupidly unfastened my seat belt,” Koch recalls. He was hoping he could run to the exit and be the first in line to get out. A few seconds later, the plane collided with an abandoned fire station, sending Koch flying forward over the unoccupied first row and into the bulkhead.

He crawled down the center of the aisle toward the back and encountered a group of people crowded there, frantic, but making little progress. He was last in line. After a couple of minutes on his hands and knees, he said to himself, “This is crazy. If I don’t figure another way out, I’m going to die.”

So he stood up, his head in the cloud of toxic smoke, and walked back, trying to hold his breath, to the front of the plane. An intense fire burned outside. “I said to myself, ‘My God, I’m going to die! What an interesting experience! I’ve done a lot of fascinating things, but I’ve never died before.’ ”

He moved to the right side of the plane, almost unconscious from the smoke, and pulled open the galley door. The emergency slide had not deployed, so he jumped out of the plane in his stocking feet, falling hard onto the pavement.

Koch spent two days writhing in pain in intensive care, suffering from smoke inhalation, with tubes passed through his nose into his lungs. Everyone who had been around him on the plane—including the elderly couple sitting to his right—had died. He was the only passenger in first class to survive.

A year passed. Having finally recovered from his crash injuries, he checked in with his doctor for a routine exam. A blood test raised red flags, and later tests would turn up a form of prostate cancer, which Koch has battled on and off for the past 16 years.

It’s taken a while, but the events of those two years—the plane crash and the cancer—have transformed David Koch, slowly changing him into one of the most generous but low-key philanthropists in America. After spending much of the past decade and a half giving to cancer causes as well as supporting his right-wing political agenda, Koch grabbed the spotlight this summer with a $100 million gift to the New York State Theater at Lincoln Center, elevating the profile of a businessman previously known mainly for a bruising fight with his twin brother over control of the family business.

Koch, who would go on to marry Julia, acknowledges that he’s now more well-known thanks to the theater gift, which capped decades of giving that has also included $125 million to his alma mater, the Massachusetts Institute of Technology, for cancer research, and $25 million to Johns Hopkins University. His giving ranks him seventh in Condé Nast Portfolio’s Generosity Index. He says the motive for much of his giving can be traced to that February evening on the tarmac in L.A. “When you’re the only one who survived in the front of the plane and everyone else died—yeah, you think, My God, the good Lord spared me for some greater purpose,” he says. “My joke is that I’ve been busy ever since, doing all the good works I can think of so he can have confidence in me.”

if you want to see David Koch, you first must talk to him. Not his assistant or his public-relations factotum, but him. No secretary manages his agenda or keeps his calendar. When I wanted to talk to financier Edmond Safra, I recall going through at least three levels of retainers, not counting an indirect approach through the Orthodox Jewish community in Brooklyn, before being allowed an audience. Penetrating Fortress Soros at the height of his bank-busting notoriety was akin to breaching the Alamo. But with Koch, one just calls his office. “This is David Koch,” a voice said later on my answering machine. “You called earlier to schedule an interview.”