Tiantian Kullander, the co-founder of the $3 billion cryptocurrency firm Amber Group, has died. He was 30. Amber announced his death on Friday in a statement published on its website. The statement says that Kullander unexpectedly died in his sleep on Wednesday. “His passing is a tragedy and our thoughts and prayers are with his family,” Amber wrote. The cryptocurrency firm, which provides its clients with liquidity and market-making services, says that Kullander was “a pillar” of its success. “He put his heart and soul into the company, in every stage of its growth,” Amber said.