Lemaitre likely gets that gold star. Slipher, with extrodinary efforts, was able to get the first real evidence for redshifting nebulae. [Recall that, back then, the view was that the MW was the extent of the Universe. Hubble was just beginning to establish that, as he called them, "extragalactic universes" were galaxies like the MW, at least the spirals.]
Lemaitre's exceptional understanding of GR allowed him to combine the evidence from Slipher and, with Hubble's new distance measurements, introduced his model -- he coined the Primeaval Atom, now known as the BBT. It broke the glass ceiling that was the Static model of the universe. [Hoyle, Gold and ???, failed to get the glass glued-back together in their Steady State model.]
Lemaitre even presented in his original paper an expansion rate for the universe, but he knew it was just a wild shot as more redshifts would be needed. These soon came from Hubble and Humason that established -- with far more accurate measurements -- many more redshifts.
But take note, following Hubble's new data, the revised expansion rate was horribly in error in spite of superior measurements. This was because Hubble, and astronomy, was not aware that Cepheids (used as a new distance measurement) came in two flavors and Hubble used the wrong one that he first found in Andromeda.