A couple of posts ago, I linked to the Wikipedia page for former world chess champion Mikhail Botvinnik (1911-1995); I'd also commend this article on the ChessBase news page as well, published a couple of days ago on the 100th anniversary of his birth. Botvinnik was a great player, but his broader contributions to the game make him an even greater figure in our game. He was the first really deep theoretician of the game, and he was also involved in training generations of top Soviet players, including Karpov, Kasparov, Shirov and Kramnik. (How's that for a collection of students?) His discussion of how to prepare for events has also proved influential, and he was even involved in the early days of chess programming, though in this case his successes were pretty limited. In all, though, he was a colossus of 20th century chess, especially in the Soviet Union, where he was known as the Patriarch.