The primeval atom was speculative and in some respects wrong. The modern Big Bang model owes as much to Gamow, Alpher, and Herman. Doesn’t calling Lemaitre the father of the Big Bang overstate his role?

The 1931 proposal was qualitative, and later work by Gamow and his colleagues gave it physical content, including the prediction of the microwave background. Lemaitre remains the first to propose that the universe began from a single primeval state and to connect the expansion law to observation, which is what is claimed here. The father title is conventional; a founder is safer, and nothing in the claim depends on which word you use.