• American Express

American Express (Photo : REUTERS/JIM BOURG)

American Express President Ed Gilligan died while on corporate plane en route to New York on May 29, Friday. Coming back from a business trip, he was said to have suddenly fallen ill while flying. He was 55 and survived by his wife and four children.

An American Express spokeswoman said the plane made an emergency landing but declined to say where Gilligan had been, according to Philly.

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Following Gilligan's death, American Express CEO Ken Chenault wrote a letter to employees, which is published in Business Wire. He said the company president's death is "deeply painful and frankly unimaginable" for all of them who had the great fortune to work with Gilligan.

In the letter, Chenault said that Gilligan loved American Express and is devoted his entire career to this company where he started as an intern 35 years ago. He also said Gilligan was "a living embodiment" of American Express's values.

Chenault further described Gilligan as a true leader and champion of diversity and employee development who eventually made his way to the top as Vice Chairman in 2007 and President in 2013.

As Chenault noted, Gilligan had contributions that left "an indelible imprint" on practically every area of the American Express business "from Commercial Card and Travel to International, Consumer, Small Business, Merchant Services, Network Services."

Earlier this year, American Express lost its exclusive relationship with Costco and lost a United States antitrust suit. In the first quarter, a stronger U.S. dollar diminished the New York credit card issuer and global payments company's revenue with its shares down 14 percent this year.