He was laid to rest on Thursday, after he fell 20 feet during a training accident in Brooklyn earlier this month.
Moon had been with the FDNY since 2002. Most of his time was spent in Queens with Ladder 133 until he transferred to Rescue Company 2, the most elite, last January.
His captain, Pat Connolly explained the magnitude of this loss. "This a guy that impacted life.. from the bottom of my heart," Connelly said
Connelly told Eyewitness News reporter Chantee Lans that Moon cared about two things, his family and helping others.
Moon leaves behind a wife and two small children, Brianne and Colin.
Inside St. Patrick's Roman Catholic Church, they gave an emotional eulogy.
"His favorite job is a fireman, but really it's being a dad," Moon's son Colin said.
"Billy you are my best friend, and you will be my forever hero. We love you. 100%," Moon's wife Kristina Moon said.
Mayor Eric Adams commended Moon and his family.
"I'm sorry that your babies are losing their dads so early," he said. "I'm sorry you're losing your spouse, but we cannot thank you enough for what your dad and what your spouse has given us in firefighter Moon."
FDNY Commissioner Laura Kavanagh, called Moon a true hero, even in death, by saving five lives, including three in New York.
One of them was for a fellow FDNY firefighter, who took Moon's lungs because he needed it to breathe after 9/11.
"Billy's lungs have literally breathed life into Terrence Jordan, made him part of Terrence's story and the story of all of those who Terrence rescued that day at the towers," Kavanagh said.
Moon set a strong example for his son who is growing his hair long to donate to sick kids.
Firefighter Moon also volunteered at the Islip Fire Department. This is the second loss for them this year.
FDNY firefighter Jesse Gerhard died in February after collapsing after a fire in Queens.
Gerhard's funeral was also held at St. Patrick's Roman Catholic Church.
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