The heroic former NYPD captain Douglas Greenwood, 61, died on Tuesday after a long battle with post-traumatic stress disorder and other painful respiratory illnesses, according to his online obituary and family friend John Feal.

"Douglas Greenwood is a hero in every sense of the world," said Feal, an advocate for 9/11 first responders. "He lived with insurmountable pain from his heroic actions."

The retired captain was one of the first people to respond to the World Trade Center after the 2001 terrorist attacks and he spent 40 consecutive days toiling through "The Pile," an infamous heap of toxic ash and debris, looking for victims, according to an online bio.

Greenwood retired from the NYPD after more than 20 years on the force to start his second career as the owner of the neighborhood favorite Bleecker Street Pizza in Greenwich Village.

The pizza shop, located at 69 Seventh Ave., has consistently ranked among New York's best slices, thanks to Greenwood's family recipe. The New York Times named the Bleecker Street parlor as one of the best slices you could get in the city.

But Greenwood suffered from "a slew" of respiratory illnesses because of his exposure to toxic dust while working at the rescue operations at Ground Zero, according to Feal.

"So many 9/11 responders are suffering physically and mentally," he said. "Douglas is not the first or the last to take his life.

"I think Douglas just didn't want to be in pain anymore," Feal added. "I pass no judgement on someone who doesn't want to live their life in pain."