(CNN)Dr. James "Charlie" Mahoney, a physician in Brooklyn for over 30 years, is another frontline casualty in the global fight against the coronavirus pandemic. But to those who knew him, he lived every day serving others and fought the virus with his endless positive spirit until he physically couldn't.
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Mahoney devoted his entire career to the University Hospital of Brooklyn, SUNY Downstate, where he began his medical schooling in 1982 and eventually worked as a pulmonary and critical care attending physician until Covid-19 sidelined him.
"He was the first one on the front lines taking the onslaught. He was our backbone," Dr. Robert Foronjy, the Chief of the Pulmonary and Critical Care Division at SUNY Downstate, told CNN.
"He saw this as his calling," Foronjy said.
Mahoney, who was 62, could have taken a back seat during the pandemic, given his age and health. But his family and colleagues say he wouldn't even consider it.
The Centers for Disease Control and Prevention has cautioned that individuals older than 60 and people with serious chronic medical conditions "are at higher risk of getting very sick from this illness."
Mahoney's daughter told CNN that she "may have been worried. And I know the rest of our family was also worried, but there was never a question of was he not going to do it."
"He wasn't going to step back and he was going to try to help people, and as many people as he could," Stephanie Mahoney said.
His patients could always reach him. He always gave them his cell phone number.
"He was almost like the mayor walking the halls of Downstate," Foronjy said.
He even had family on campus. His older brother Dr. Melvin Mahoney is an internal medicine physician at the hospital. They'd often get each other's hospital pages, his daughter said.
Known best as "Charlie", Mahoney was also a clinical assistant professor at the academic hospital. He supervised and mentored countless medical students throughout his career.
"Sometimes he did it by giving someone a pat on the back and sometimes when they needed a dressing down, but they were always getting the truth from him and they always knew that he cared," Foronjy said.
Vytas Vaitkus, a pulmonary critical care fellow, trained under Mahoney for seven years during his time at SUNY Downstate.
Vaitkus was nervous to present a patient to Mahoney his first year as an intern in 2013, because his excellent reputation preceded him, but Mahoney took care of that quickly.
"Before I started he cut me off and started talking about a story. He made me feel completely at ease right away," Vaitkus recalled.
Mahoney's kids agreed.
"My dad was a big story teller," Stephanie said. "He would always tell these stories and he would be so vibrant and so funny and he would be really truly like a character."
Mahoney brought that energy to the physically and mentally taxing treatment of critically ill Covid-19 patients at the beginning of the pandemic.
New York City is considered an epicenter of the virus, with more than 191,000 cases since March, according to city data.
All the patients at SUNY Downstate have suffered from Covid-19 -- it's one of three hospitals in the state ordered by Gov. Andrew Cuomo to dedicate itself entirely to dealing with the pandemic in late March. Four patients died of the virus in one hour that CNN visited SUNY Downstate in early April.
"One of those days in the early kind of beginning, he called me and just was like, 'you know Steph, this has been one of the hardest days I've ever had in in medicine,'" his daughter said.
Though he worked day shifts at SUNY Downstate, nights at Kings County Hospital Center and served an outpatient practice, Mahoney's kids saw him as ubiquitous.
Mahoney has three children, Jamie, 31, Stephanie, 27, and Ryan, 25.
"You would've thought he had more hours in the day than anybody,