H.M. died on Tuesday. He was a severe amnesiac. At the age of 27 he underwent surgery to correct severe and debilitating seizures. When he awoke, he was unable to remember much of anything ever again–at least not anything in the declarative memory system.
He lived life as the most famous experimental subject in the history of cognitive psychology and neuroscience. I remember reading about him when I was a graduate student in the late 1980's and 1990's. What researchers learned by studying him was that there was more than one memory system. This information led to a revolution in our understanding of human cognition and learning.
After years being known only as H.M., to protect his identity, in death we learn that his name was Henry Gustav Molaison, and he lived his life in Connecticut, on the east coast of the United States.
The New York Times tells his story better than I can. It is well worth the read.
And NPR has a previous story, that you can hear. It is well worth the listen.
And here's H.M.'s wikipedia entry.