Thousands of first responders and mourners gathered Monday at the Cathedral of the Holy Cross in the South End for the funeral of Robert ‘BK’ Kilduff Jr., a Boston firefighter who died in May while battling a fire in Dorchester.

The funeral began just after 10 a.m., with firefighters from across the country and Canada in attendance.

“Every day, he embodied what it means to be a good neighbor, a caring friend, an empathetic stranger. Nobody was out of the bounds of his compassion,” his daughter, Hannah Jane Kilduff, said during her remarks. “To say that I’m proud of my dad is an understatement, but I’ll say it anyway.”

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Even as a child, she said she knew her dad was “one of the helpers.”

“Whether he was showing up to rescue the people of Boston, to coach the youth of West Roxbury, or to support his own kids, he was the man you could look for in the crowd who would stop at nothing to help make you feel better,” she said. “My dad represents everything our world can be if we look out for each other — if we reach out to help first, and ask questions later.”

On May 23, Kilduff was one of the firefighters who responded to a three-alarm fire in Dorchester. While trying to extinguish the fire, Kilduff fell three stories and was taken to a hospital where he was later pronounced dead. His death remains under investigation.

Kilduff served as a Boston firefighter for 24 years and was the first to die in the line of duty in more than a decade. He was a member of Rescue Company 2, located at Egleston Square station in Roxbury.

Kilduff’s son, Mason Kilduff, said he and his father were “Boston guys forever” and shared a great connection over sports and their love for the city.

“I was always so proud to call him my dad. He was the one front and center when it came to helping someone,” he said. “But the greatest thing that I get to claim about my dad was that he was my best friend.”

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He said his dad “loved building community” and lived his entire life driven by his love to give back.

“My dad is my hero,” he said. “He’s the hero everyone says he is, and I’ll miss him forever. And he taught us all how to live, and now he’s taught us how to die.”

Boston Fire Commissioner Rodney Marshall was one of multiple fire and city officials who gave remarks.

“One of the best compliments that a firefighter can pay to another firefighter is to call him a good jake,” he said. “BK was a jake’s jake.”

Marshall calls Kilduff’s death a tragedy “that is certainly felt by all of us,” and that he will be “sorely missed.”

Firefighter Vic Gaybor said Kilduff was a prankster at the firehouse but got serious when it was time to get to work.

“It was time to get serious and do what was asked of us to get the job done. And BK was the one I wanted by my side,” he said. “BK was an exceptional firefighter, if not one of the best, the best. His courage was unmatched by anyone.”

Lieutenant Greg Kelly, another firefighter who worked with Kilduff, said his death is “leaving such a hole” in this crew.

“I take a lot of comfort in knowing that he was doing what he loved so much at the time his life was lost,” he said. “His very last act was actually to yell up to the Ladder 4 and Ladder 6 roof men to back it up because they were working in an intersection of the building that was unsupported due to the fire.”

Boston Mayor Michelle Wu offered her “deepest condolences” to Kilduff’s family and said he “gave his life making sure his neighbors got another day.”

“Because of Bobby Kilduff, five of our neighbors will get to spend more time with the people they love,” she said. “That’s his legacy. It lives on in everyone who got another day with their loved ones because he answered the call.”