Most Proficient King's Indian Player?

@BronsteinPawn: Bronstein clearly deserves a place at the throne in the KID Hall of Fame.

@Santero13: Geller should be right beside him.

I offer a third member of the KID Triuvirate -- Svetozar Gligorić. My evidence in support of his inclusion comes from his games and from this testimony by Bronstein, commenting on Averbakh--Gligorić, Zurich 1953, after White's 14th move: "Now Black can only defend the d-pawn by tactical means, since 14.. Rd8 obviously loses to 15 B:c5. Gligoric proves equal to the challenge: his is not a mechanical but a creative mastery of every nuance of the King's Indian."

Bronstein, Geller, Tal, Fischer, and Kasparov were probably the biggest devotees of the KID, and from the white side, let's not forget Reshevsky--he used to crush the KID.  Today, Naka and Ding Liren play it most often.  To learn it, Zurich 53 and My 60 Memorable Games will cover most of what you need in the KID.

Gelfand-Nakamura (World Team Championship) was an insane KID game.

kasparov, nakamura, fischer, and Miguel Najdorf

Bronstein, Fischer, Tal, Kasparov.