Pavel Sergeyevich Alexandrov was born before Grigory Margulis.
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. 
