Stephen Blyth

Blyth, 48, had been out since May on a previously reported medical leave. His resignation was effective immediately, bringing to a close a brief and tumultuous tenure at the top of the world’s largest educational endowment. Harvard Management Co. said operating chief Robert A. Ettl will remain interim chief executive. The Harvard Management board has hired a search firm, David Barrett Partners, to find a replacement for Blyth. A London native and Harvard PhD statistician with a big personality, Blyth took over as chief of the fund at the beginning of 2015, charged with improving performance. He proved to be a controversial figure, changing the endowment’s investment approach and cutting some high-level staff, while also facing the surprise departures of some talented managers. A former Wall Street executive, he kept a trading desk in the endowment’s main room, high in the Federal Reserve tower downtown. Blyth followed Jane Mendillo, who inherited the chief executive job just as the financial crisis hit, and was credited with being a calm hand at the wheel during a period of deep investment losses and a cash crunch. Prior to Mendillo, the fund was managed by Mohamed El-Erian, who left in December 2007 after nearly two years on the job, as the subprime mortgage market was collapsing, to rejoin Pacific Investment Management Co., or Pimco.