King's Indian: 4.Bg5 O-O

King's Indian: 4.Bg5 O-O

Definition

The sequence 1. d4 Nf6 2. c4 g6 3. Nc3 Bg6 4. Bg5 O-O defines one of the so-called “early bishop” systems against the King's Indian Defence (ECO code E60). White immediately pins the f6-knight with 4.Bg5; Black replies with the thematic 4…O-O, ignoring the pin in order to complete development and prepare …d6 or …c5. The variation is sometimes called the “Rare 4.Bg5 System” or the “Pseudo-Trompowsky” because the bishop emerges on g5 in a position that still contains the characteristic KID pawn structure.

Typical Move Order

One common tabiya arises after:

• 1.d4 Nf6
• 2.c4 g6
• 3.Nc3 Bg7
• 4.Bg5 O-O
• 5.e3 d6
• 6.Nf3 c5, when both sides have reached a flexible structure with plenty of independent play.

From moves 5–10 the game can transpose into several families: a Fianchetto Grünfeld, a Saemisch-like pawn storm (if White plays f3 and e4), or even Catalan-flavoured positions after g3. This “chameleon” nature is one reason many champions occasionally adopt the system as a surprise weapon.

Strategic Ideas

• For White
  • Exploit the pin by preparing Qd2, f3, and if possible e4, gaining space while delaying the usual KID structures.
  • Keep the option of cxd5 to undermine Black’s center if Black plays …d6–d5.
  • Occasionally double Black’s f-pawns with Bxf6, leading to an endgame where Black’s bishop pair is offset by structural weaknesses.
• For Black
  • Break the pin tactically: …h6 & …g5, or positionally by …d6 followed by …Nbd7 and …e5.
  • Use the extra tempo from White’s bishop sortie to strike in the center with …c5 or …d5 before White marshals an e4 advanced center.
  • Capitalize on the uncommitted White king (often still on e1) to open the position at a moment of Black’s choosing.

Historical Context

The line was first played at master level in the 1940s. It briefly gained popularity in the 1960s when Bobby Fischer tested it twice with White, most famously in Fischer–Larsen, Bled 1961, a sharp draw. In the 1990s the system resurfaced as a surprise choice by Garry Kasparov and Alexei Shirov, who valued its ability to avoid well-trodden Classical KID theory.

Illustrative Game

Kasparov – Anand, Dortmund 1996

Kasparov employed 4.Bg5 specifically to escape Anand’s deep preparation in the Mainline Mar del Plata. The middlegame became an unbalanced struggle revolving around the IQP on d4, highlighting the variation’s dynamism.

Sub-Variations

1. 5.e4 d6 6.Nf3 – The position can transpose back into the classical KID but with the bishop already on g5, offering fresh resources.
2. 5.Nf3 d5 – Leads to hybrid Grünfeld/KID structures.
3. 5.Qd2 d6 6.Nf3 – White commits to queenside castling and a pawn storm with h4-h5.

Interesting Facts & Anecdotes

• Grandmaster David Bronstein recommended 4.Bg5 as early as 1955, suggesting that “the soul of chess is surprise.”
• Because the bishop move is the 4th ply, database statistics are thin; many players meet it “over the board” without concrete preparation.
• Computer engines initially disliked the line for White, but neural-network engines (e.g., Leela Zero) reevaluate it as fully playable, proving that strategic complexity can confound brute-force approaches.

When to Choose This Line

Opt for 4.Bg5 O-O if you want to:

• Sidestep memorized mainlines like the Classical, Saemisch, or Fianchetto Variations.
• Maintain transpositional flexibility while testing your opponent’s strategic understanding.
• Create asymmetrical pawn structures and avoid early forced draws.

Conclusion

The King’s Indian: 4.Bg5 O-O is an offbeat yet strategically rich choice. It offers White the chance to dictate the character of the game while confronting Black with unique problems unseen in mainstream KID lines. Although not as extensively analyzed as 4.e4, its surprise value and strategic depth make it a valuable addition to any 1.d4 player’s arsenal.