Tristan O’Tierney, a co-founder of the mobile payment company Square, has died after a years-long struggle with addiction. He was 35.

O’Tierney had been undergoing treatment at a rehabilitation facility in Ocala, Fla., the San Francisco Chronicle reported. Pamela Tierney told the newspaper that her son’s Feb. 23 death was related to his addiction: “I know he got to the hospital, he couldn’t breathe and they couldn’t revive him,” she said.

O’Tierney is the second prominent tech leader in recent months to die suddenly. Colin Kroll, the co-founder of the gaming app HQ Trivia and the now-defunct video app Vine, died in December in what police suspect was a drug overdose.

Square co-founders Jack Dorsey and Jim McKelvey hired O’Tierney to develop the company’s first mobile app in 2009. O’Tierney framed that effort in empowering and democratic terms: “I helped start a company called Square to let regular folks accept credit cards just like the big boys,” he wrote on his personal website.

Square, which offers businesses a suite of mobile payment and payroll tools, reported nearly $1 billion in revenue during its most recent earnings report. It was ranked among the 20 most popular free apps in the Apple store in 2018.

O’Tierney left the company in 2013. He previously worked for Yahoo and Apple, according to his website, and had recently taken up travel photography.

In a September Twitter post, O’Tierney said his work at Square had “set me up for life,” but that his battle with addiction was taking a toll.

“As some of you may know, I’ve been battling with addiction for these past few years. With some success. A lot of failure too though."

In a statement, Square said: “Tristan was part of Square’s founding story and we are deeply saddened by his passing. Our thoughts are with his family and friends.”

In recent years, addiction experts have noted a growing problem among tech workers whose industry is marked by intense competition, grueling deadlines and new personal wealth. According to a report from the San Jose Mercury News, drug use and addiction are now a part of the sector’s landscape, but that an insular, work-obsessed culture has partially masked the severity of problem.

O’Tierney is survived by his daughter Rumi Ari; his girlfriend, Anjela Ramos; his parents, Mark and Pamela Tierney; and sister, Terri Lynn Cloud, according to the report.

Showcasing his photography on his website, O’Tiereney wrote: “I turned my passion for building artistic iPhone apps, and turned it into just art. I hope you enjoy.”