Ernest McCulloch, who was part of the scientific duo that first identified a stem cell, died Jan. 20 at the age of 84. The New York Times‘s obit was full of amusing personal details (his nickname was Bun) while The Washington Post’s obit (whose link is m.i.a.) did a nice job conveying the eureka moment of his discovery. With his longtime collaborator James E. Till, he made one of the biggest contributions to medical science in the last 100 years by being the first to figure out, in the 1960s, that all three types of blood cells–red cells, white cells, and platelets– are produced by a single stem cell. The politicized controversy surrounding embryonic stem cell research obscures the enormity of this discovery, without which we would not have bone marrow transplants and a springboard for innovative future treatments for various cancers, Alzheimer’s disease, diabetes, cardiovascular disease, spinal cord injuries, and many other ailments. Part of what makes their story so amazing is that as with so many great discoveries, this one was accidental: the pair were actually trying to figure out how radiation exposure from nuclear weapons killed and how radiation destroyed tumors. After injecting bone marrow cells into mice, they noticed that in the survivors, somehow forming new colonies of blood cells.