Colin Kroll, co-founder and CEO of the hit gaming app HQ Trivia, was found dead Sunday morning in New York. He was 34 years old.

Police found Kroll in the bedroom of his New York apartment, after Kroll’s girlfriend called the New York Police Department asking for a wellness check, a law enforcement source told CNN.

“We learned today of the passing of our friend and founder, Colin Kroll, and it’s with deep sadness that we say goodbye,” a spokesperson for HQ said in an emailed statement. “Our thoughts go out to his family, friends and loved ones during this incredibly difficult time.”

Kroll was unconscious and unresponsive and pronounced dead on the scene. Police notified his family, according to New York Police Detective Ahmed Nasser. The Medical Examiner will determine the cause of death.

Kroll became a big name in the tech world after co-founding Vine, the now-defunct looping video platform that launched the careers of numerous social media stars.

Twitter bought Vine in 2012 and shuttered the platform four years later.

Kroll and business partner Rus Yusupov went on to form Intermedia Labs, the company behind HQ Trivia. The real-time trivia game app launched in 2017 and was a breakout success. It soared to the top of Apple’s free game app chart in the first couple months of 2018.

But its popularity has waned — it has fallen out of the top 100 free games list on the iTunes app store.

Intermedia Labs is reportedly in turmoil as it’s struggled to reengage an audience.

Recode reported that Kroll worked with another board member to oust Yusupov, who served as CEO. Kroll then became the CEO after Yusuprov was forced out.

As he prepared to take on the role, questions about his conduct triggered concern. A formal HR complaint accused him of “inappropriate and unprofessional” behavior, Recode reported, and sources told the outlet Kroll was previously fired from Twitter for poor management.

Intermedia Lab told Recode that a third-party investigation into the complaint “yielded no concerns.”