John Grefe, an American IM and United States co-champion in 1973, died earlier today (Sunday) at the age of 66. Grefe will be unknown to most players outside the U.S., and even to those inside the U.S. as well unless their chess careers or their knowledge of American chess goes back to the 70s and early 80s, but he was considered quite a talented player back in his day. He seems to have given up on serious play in 1981, and while that was probably the right thing decision financially it was a pity for chess, as he had a very lively style. (Have a look at the games given and linked to in his Wikipedia article for ample evidence.)
My condolences to his friends and family.