Gregori Aleksandrovich Margulis (Russian: Григо́рий Алекса́ндрович Маргу́лис, first name often given as Gregory, Grigori or Grigory; born February 24, 1946) is a Russian mathematician known for his work on lattices in Lie groups, and the introduction of methods from ergodic theory into diophantine approximation. He was awarded a Fields Medal in 1978 and a Wolf Prize in Mathematics in 2005, becoming the seventh mathematician to receive both prizes.