Carl Friedrich Andreyevich von Jaenisch (Vyborg, April 11, 1813 - Saint Petersburg, March 7, 1872) was a Finnish and Russian chess player and theorist. In Russian, he was known as Яниш (‘Yanish’) although a phonetic translation of the original German name would have been ‘Ениш’. In the 1840s, he was among the top players in the world.
He began a military career in Finland, but soon moved to Russia to teach rational mechanics in Petersburg (now Saint Petersburg). He dedicated his life to mathematics and chess, two subjects which he considered closely related. He tried to show their connections in his work Découvertes sur le cavalier (aux échecs), published in Petersburg in 1837.
In 1842-43 he published a book on the openings in two volumes: Analyse Nouvelle des ouvertures. In 1862-63 he published his major work: Traité des applications de l'analyse mathématique au jeu des échecs, in three volumes.
He wanted to take part in the London 1851 chess tournament, but arrived late and instead played a match with Howard Staunton, which he lost (+2 -7 =1). Three years later he also lost to Ilya Shumov (+3 -5 =4).
Jaenisch is best remembered for having analyzed and helped develop Petrov's Defence with Alexander Petrov, and for his work on the Schliemann-Jaenisch Gambit of the Ruy Lopez, which begins 1. e4 e5 2. Nf3 Nc6 3. Bb5 f5!? The dubious gambit 1.c4 b5 is sometimes referred to as the Jaenisch Gambit; Jaenisch mentioned this move but did not advocate it.
Staunton was most upset at his death in 1872, writing to Tassilo von Heydebrand und der Lasa in November of that year:
Ilya Shumov vs Carl Friedrich von Jaenisch, St Petersburg (1845), Italian Game, a game later attributed to Pope Leo XIII.