Short answers, pulled from the story.
Georges Lemaître proposed in March 1931 that the universe began as a single initial quantum, which he called the "primeval atom." He argued that the cosmos expanded outward from this point, making it the first formulation of what is now called the Big Bang theory.
When Lemaître presented his 1927 paper on an expanding universe, Einstein told him: "vos calculs sont corrects, mais votre physique est abominable" - meaning his calculations were correct but his physics was abominable. By 1933 at the California Institute of Technology, Einstein stood and applauded after Lemaître's presentation, though historians note uncertainty about exactly what aspect of the theory Einstein was praising.
Lemaître published his 1927 paper in the Annales de la Société Scientifique de Bruxelles, a journal that was not widely read by astronomers or physicists outside Belgium. Edwin Hubble's 1929 paper on the same relationship, published in the Proceedings of the National Academy of Sciences, reached a far wider audience and drew the attention that Lemaître's work did not.
In 2018, the International Astronomical Union voted 78% in favor of recommending that the law be called the Hubble-Lemaître law, recognizing that Lemaître had independently derived the proportional relationship between galactic recessional velocity and distance in 1927, two years before Hubble published his more widely read paper on the same finding.
Lemaître firmly rejected concordism - the effort to align theological and scientific knowledge - arguing that the Bible is not a textbook of science. He viewed his cosmological work as neither supporting nor contradicting Catholic faith, and he successfully persuaded Pope Pius XII not to make further public statements linking the Big Bang to the doctrine of creation after a 1951 papal address drew that parallel.
Shortly before his death, Lemaître learned from his assistant Odon Godart that radio astronomers Arno Penzias and Robert Wilson had detected the cosmic microwave background. Lemaître died on the 20th of June 1966. That discovery convinced most experts of the scientific validity of the Big Bang, the theory Lemaître had first proposed in 1931.