For Guess the Grandmaster #6 the answer I intended was Efim Geller. - His peak ranking was outside World No. 1, and he never played a World Championship match. - He had an incredible record against World Champions, scoring classical wins over Botvinnik, Smyslov, Tal, Petrosian, Spassky, Fischer, Karpov, and Kasparov. - The Geller Defense (1.d4 Nf6 2.c4 b6) bears his name, although it's much less common than defenses like the King's Indian or Grünfeld. I will admit, though, that this clue set wasn't as clean as it should have been. Saying "a defense against 1.d4 remains a mainstay at every level" was misleading because the Geller Defense is relatively uncommon today. That made Grünfeld a much more natural thought process than Geller. So let me do one that's precise enough to have one clear answer. Hint 1 This grandmaster has never crossed 2700. Hint 2 Despite that, they have defeated every undisputed World Champion from Smyslov through Anand in classical chess. Hint 3 They are famous not because of a single opening, but because they authored one of the most influential chess books ever written, a book that many grandmasters still recommend. Who is it?

..? @Mayne B

Luka's pfp is my friend's pfp ha, not even the same app