When massive stars die, they explode in violent spectacles known as supernovae, specifically core-collapse supernovae. These cataclysmic events produce and distribute a large fraction of the heavy elements in the universe, but the properties of the massive stars that produce them have historically been difficult to measure. I have made new measurements constraining the masses of stars that have produced core-collapse supernovae, also known as supernova progenitors. I have done this by measuring the ages of stars at the location of supernova remnants: the nebulae of excited and enriched gas left behind by supernovae that have occurred over the past 20,000 years. Assuming the progenitor was associated with these stars, I am able to estimate the age of the star that exploded. Using theoretical models, I am able to infer the mass from this age. I used images taken by the Hubble Space Telescope to investigate the stars responsible for producing hundreds of these remnants in the nearby galaxy NGC 6946. In addition to the remnants of supernovae, this galaxy has hosted ten observed core-collapse supernovae within the past hundred years, leading to it being referred to as the “Fireworks Galaxy”. I was able to constrain the progenitor mass distribution for 175 remnants, eight of the historically observed supernovae, as well as the progenitor of the first direct black hole formation candidate in NGC 6946. I found the distribution of progenitor masses was consistent with mass distributions measured for massive stars in other galaxies, including our own Milky Way. These new measurements allow NGC6946 to be included for the first time in statistical studies of the masses of stars that produce supernovae.