Patrick Byrne, a rare champion of cryptocurrencies among the heads of public U.S. companies, has stepped down from his roles at Overstock.com.

Byrne

wrote in a letter to shareholders Thursday that he was stepping down from the company both as CEO and as a member of its board of directors due to insurability and other reasons after admitting to a three-year relationship with Maria Butina, a Russian agent currently serving 18 months in prison after pleading guilty to charges of acting as a foreign agent.

He will be replaced on an interim basis by Jonathan Johnson, the current president of Overstock's blockchain initiative Medici Ventures, a press release said Thursday.

"In his twenty years as Overstock’s leader, Patrick’s vision for Overstock as an innovation leader has come to fruition," Johnson said in a statement. "It will be my mission as I take the helm to continue and build on Overstock’s achievements and success."

Johnson added that "I am confident Overstock’s future – both in retail and blockchain – is bright."

Byrne said Johnson is "prepared ... to successfully oversee both our retail and blockchain businesses" in the press release.

While acting as interim CEO, Johnson will continue to serve on the board of directors for both Medici Ventures and the company's security token trading platform tZERO, as well as act as president of Medici.

Patrick Byrne image via CoinDesk archives