Byrne has a long history of medical problems after a long bout with cancer nearly 30 years ago. Due to the cancer and related heart problems, Byrne says, he has undergone more than 106 surgeries over the last three decades. And in the last year, he has battled a recurrence of Hepatitis C, which he first contracted on a visit to China in the early '80s. "I've been really gutting it out over the past few months," he says.

His decision to take a leave of absence from Overstock—a cut-rate online retailer based in Salt Lake City, Utah—will be felt most among the worldwide community working to advance bitcoin and the bitcoin blockchain, the vast digital ledger that underpins the digital currency.