The Big Bang theory was first proposed by Georges Lemaître, a Belgian priest, physicist, and astronomer, in 1927. He suggested that the universe began from a single, incredibly dense and hot state he called the “primeval atom,” from which expansion occurred. This idea was later supported by empirical evidence such as Edwin Hubble’s observations of galactic recession, which aligned with the notion of an expanding universe. The theory was further developed and popularized by other scientists, including George Gamow, helping to shape modern cosmology.