Superrigidity is a discovery by a mathematician. Pavel Sergeyevich Alexandrov was born 2 years before this mathematician.
Pavel Sergeyevich Alexandrov (Russian:    ), sometimes romanized Paul Alexandroff or Aleksandrov (7 May 1896  16 November 1982), was a Soviet mathematician. 
Gregori Aleksandrovich Margulis (Russian:    , first name often given as Gregory, Grigori or Grigory; born February 24, 1946) is a Russian-American mathematician known for his work on lattices in Lie groups, and the introduction of methods from ergodic theory into diophantine approximation. 
 That this phenomenon happens for certain broadly defined classes of lattices inside semisimple groups was the discovery of Grigory Margulis, who proved some fundamental results in this direction. 
