Howard Marks was failing miserably. It was 1977, and the research group he oversaw at Citibank had recommended Nifty 50 stocks that lost 90 percent of their value over the previous decade. Peter Vermilye, Citibank’s chief investment officer, gave Marks an option: He could quit research and start a fund focusing on convertible bonds, a niche where neither the New York bank nor Marks had any experience.