Purnell Choppin, virologist and head of institute that funds medical research, dies at 91

The institute was founded in 1953 by Howard Hughes, the reclusive billionaire, aviator and Hollywood producer. For decades, it was under the umbrella of the Hughes Aircraft Co. When that company was sold in 1985 for more than $5 billion, the medical institute was suddenly one of the richest philanthropic organizations in the world. Dr. Choppin, who began as chief scientific officer, became the institute’s president in 1987.