Lionel Adalbert Bagration Felix Kieseritzky (; – ) was a Baltic German chess master and theoretician, famous for his contributions to chess theory, as well for a game he lost against Adolf Anderssen, which because of its brilliance was named "The Immortal Game". Kieseritzky is the namesake of several openings and opening variations, such as the Kieseritzky Gambit, Kieseritzky attack, and the Boden–Kieseritzky Gambit.