Ed Koch, the mayor who helped steer New York City away from bankruptcy, has died at age 88 on Friday morning.

Koch's spokesman, George Arzt, said the former mayor died at 2 a.m. from congestive heart failure at New York-Presbyterian/Columbia Hospital.

In December, Koch was battling pneumonia and was taking antibiotics when he was recently admitted into the hospital for water in his lungs, according to the Associated Press.

The mayor first took office in New York on Jan. 1, 1978. He helped restore the city's credit with unwavering enthusiasm and willpower.

"I'm the sort of person who will never get ulcers," Koch once explained, according to AP. "Why? Because I say exactly what I think. I am the sort of person who might give other people ulcers."

Following his death on Friday, Twitter and other social media sites were flooded with messages of sorrow and tributes to Koch, including from celebrities and fellow politicians.

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CNN television show host Piers Morgan posted, "So sad to hear about Ed Koch. Great Mayor, great man. I interviewed him 3 weeks ago – we'll run it tonight as a tribute. CNN 9pm/ET."

Celebrity chef Bobby Flay also posted his grief to Twitter.

"Ed Koch was my mayor," started the Food Network star. "Watched him campaign at the 77th st subway station to get elected. He was also an enthusiastic foodie. Will be missed."

"30 Rock" star and New Yorker Alec Baldwin added, "RIP Ed Koch, as much a part of NY as Central Park, hot dog carts, the Yankees, the subway. A mayor of the people like few others."

New York City's current mayor, Michael Bloomerg, also took to Twitter about Koch.

"Ed Koch's spirit will live on here at City Hall, on the bridge bears his name, and all across the five boroughs," said the mayor.

Mayor Bloomberg added, "RIP @MayorEdKoch. NYC will miss you dearly," after noting that Koch was a "great mayor, a great man, and a great friend."

Coincidentally, the documentary based on Koch's life was released in New York City on Friday, the same day as his death.

Bloomberg said the former mayor "is probably laughing somewhere up there" about the timing, according to ABC News.