Len prepared for Princeton at the Hun School. At Princeton, he majored in biology, was elected to Phi Beta Kappa, and graduated with high honors. Len rowed crew and was a member of the International Relations Club and the Student-Faculty Association.
After graduation, he taught at Hotchkiss School for two years before receiving a medical degree from the University of Rochester School of Medicine. From 1943 to 1945 he served in the Navy.
Throughout his career Len was known as an ardent and caring doctor and teacher who spent his personal and professional life trying to improve the lives of others. He was an instructor in medicine and cancer research at Rochester’s medical school; director of medicine at the National Cancer Institute; and professor, dean, and director of Strong Memorial Hospital of the University of Rochester.
In 1984, after retiring as senior vice president for medical education and science policy at the American Medical Association in Chicago, Len joined the medical school faculty at Northeastern University, where he continued teaching, even from his hospital bed, until three weeks before he succumbed to pneumonia.
Leonard married Jane Thomas in 1943. He is survived by Jane; their children, David M. and Anne R. Fenninger; four grandchildren, Kathy O’Donnell, Randolph Wolfe, Heather Fenninger, and Brandon M. Fenninger; and four great-grandchildren. To them all, the class extends sincere sympathy.