Hubble discovered that other galaxies existed

I knew Edwin Hubble for discovering galaxy redshifts (1929), showing the universe was expanding. What I did not know was that just 6 years prior, it wasn't known that other galaxies even existed! It was Hubble who proved some there were galaxies beyond our own. This had long been suspected, yet it had not been the prevailing view.

Source: https://en.wikipedia.org/wiki/Edwin_Hubble