Alexander Friedman (1888-1925) was a Russian, Jewish, mathematician and astronomer. His main contribution to science is positing, in 1922, the hypothesis that the universe is expanding.
Edwin Hubble’s 1929 observations proved this hypothesis to be correct.
Since Albert Einstein’s special relativity there had been a debate as to whether the universe is static or expanding. Lamaitre’s Big Bang hypothesis of the origin of the Universe and Edwin Hubble’s telescopic observations eventually demonstrated that the universe began at one point and is expanding outwards.
The detection of cosmic microwave background radiation also lead to the abandonment of Einstein’s steady state hypothesis of the universe.
Freidman and others contributed to the elucidation of Einstein’s homogeneous and isotropic universe (that the universe is the same everywhere in the sense that the same physical principles apply everywhere in it). The set of equations and proof of the homogenous universe is called the Freidman-Lamaitre-Robertson-Walker metric or FLRW metric.
Alexander Friedman. Uber die Moglichkeit einer Welt mit konstaner negativer Krummung des Raumes, Z Physics 21. (1924)