At the start of Wednesday's play at the Sinquefield Cup, it was announced that Latvian grandmaster Evgeny Sveshnikov had passed away on Wednesday at the age of 71. Sveshnikov was never close to becoming a world champion (though he was perhaps the equivalent of today's high-2600/borderline-2700 GM in his peak years), but when it comes to his influence on the game - in the opening in particular - he was one of the most important chessplayers of his time.
His contributions to opening theory are legendary - most famously in the system that bears his name (1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e5, particularly 6.Ndb5 d6 7.Bg5 a6 8.Na3 b5), but also the Kalashnikov Sicilian (which may also have deserved to be named for him: 1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 e5 5.Nb5 d6), the 2.c3 Sicilian, and the Advance Variation against the French.
Off the chessboard, he was also known for his perennial but unsuccessful crusade in favor of copyrighting chess games. Like Emanuel Lasker's try before him, the attempt was doomed to failure. (You're welcome to debate the merits of his proposal in the comments; I'm glad that the attempt has failed, but sympathize with it. Somewhere, probably on an earlier version of the blog many years ago, I believe I critiqued some version of the plan.) That he argued for this somewhat capitalistic idea when he was a citizen of the USSR - an irony noted by Yasser Seirawan during the Sinquefield Cup broadcast - shows his courage and his independent cast of mind.
Here is ChessBase's obituary, Chess.com's, and the New York Times's. And it's also worth your time to see the discussion of Sveshnikov in the round 2 broadcast, from around 9:15 in through 16:25 and then from 33:15 through 37:30 or so. (A note about the game Ashley shows: Sveshnikov was playing "his" variation at least nine years beforehand.)