I will unusually start this endgame article with an opening:
Yes, it is Ruy López, Morphy Defense, Exchange Variation. The very same opening White used in the famous game Lasker vs. Capablanca, St. Petersburg 1914, to achieve an unexpected and sensational victory against the “unbeatable” Cuban genius.
Why do I mention it here? Note the pawn structure – White dominates the king side (four pawns against three), while the black pawns on the queen side are fully blocked by the white ones, thanks to the doubled pawns on the d-file. Let’s have a look at the possible outcome that could appear at the endgame:
Did I say that the doubled pawns are weak? It is true in most cases, but every rule has an exception. Let’s analyze another pawns vs. pawns endgame, where the doubled pawns are actually the key asset to win: