Segalovich and Yandex CEO Arkady Volozh founded the company in 1997 and built it into the leader of the Russian internet search market, ahead of U.S. rival Google. In 2011, Yandex raised $1.4 billion in an oversubscribed initial public offering in New York and it currently has a market value of $10 billion. Segalovich had been diagnosed with a treatable form of cancer and was responding well while working a full schedule, before unexpectedly having complications, Yandex said.