A firefighter among the first responders after the September 11 attacks, who then battled illness in the years that followed, has died.

The Uniformed Firefighters Association says Ray Pfeifer died from cancer he got as a result of his time at the World Trade Center site. Pfeifer spent 27 years with the department, and went on to become a key advocate of the Zadroga Act, which provides health care to first responders who got sick after the attacks.

The UFA praised Pfeifer for making the FDNY stronger, saying in part:

"Ray Pfeifer was the bravest of the brave. He was selfless in his work on behalf of Firefighters and first responders in the aftermath of the 9/11 attack. Even in his final act — helping raise money for a wheelchair-accessible van to transport firefighters to and from hospital visits."

Tributes poured in on Twitter. Mayor de Blasio wrote:

Senator Charles Schumer also tweeted about Pfeifer, writing:

Pfeifer leaves behind a wife and two children. He was 59-years-old.