Brian Sutton-Smith, a major contributor to the study of play and a pioneer in researching it -- and author of 50 books and 350 scholarly articles -- passed away due to complications from Alzheimer's disease this past Saturday, aged 90.
Sutton-Smith had most recently held a 17-year professorship at the University of Pennsylvania; he remained Professor Emeritus at that institution until is death.
Sutton-Smith is influential and has been widely cited. One notable example (found here on Gamasutra) is Jane McGonigal's popular book Reality is Broken.
Sutton-Smith's papers and library make up much of the Brian Sutton-Smith Library and Archives of Play at the The Strong National Museum of play, in Rochester, New York. The institution calls him "America’s foremost play scholar."
You can find a much more detailed obituary at Valley News; Johann Sebastian Joust developer Douglas Wilson tweeted a book recommendation in response to the news, calling Sutton-Smith's The Ambiguity of Play his top recommendation for a "scholarly book on play/games."