The Fischer Defence to the King's Gambit is a chess opening variation that begins with the moves: 1. e4 e5 2. f4 exf4 3. Nf3 d6
Although 3...d6 was previously known, it did not become a major variation until Bobby Fischer advocated it in a famous 1961 article in the first issue of the American Chess Quarterly.
After Fischer lost a 1960 game at Mar del Plata to Boris Spassky, in which Spassky played the Kieseritzky Gambit, Fischer left in tears and promptly went to work at devising a new defense to the King's Gambit. In Fischer's 1961 article, "A Bust to the King's Gambit", he claimed, "In my opinion the King's Gambit is busted. It loses by force." Fischer concluded the article with the famous line, "Of course White can always play differently, in which case he merely loses differently. (Thank you, Weaver Adams!)" The article became famous.
Remarkably, Fischer later played the King's Gambit himself with great success, including winning all three tournament games in which he played it. However, he played the Bishop's Gambit (1.e4 e5 2.f4 exf4 3.Bc4) rather than the King's Knight Gambit (3.Nf3), the only line that he analyzed in his article.