Massive stars, with an initial mass of 8 Solar masses or more, make up less than 1% of the stellar population, but play a major role in shaping the universe. The most massive stars known reside in the cluster R136 in the Large Magellanic Cloud, a satellite galaxy of our Milky Way lying at a distance of about 150.000 light years from Earth. We have used the Hubble Space Telescope to obtain the spectral light distribution of over 50 stars in the cluster, and with these observations constrained the stellar properties. For this, we compared the observations with advanced theoretical models. We find that the stars in R136 have masses reaching up to 240 Solar masses. We also find that the stars exhibit strong outflows of plasma that reduce the stellar mass over time. We have studied these so-called stellar winds and find them to be extremely inhomogeneous or “clumpy”. Using this information, we compute how the stars in the cluster evolve over time: we are able to link the current mass to the initial mass and predict the future and final fates of the stars. Lastly, we measure the extinction of the stellar light due to dust. Insight into the dust properties aids the mass measurements and gives us a better understanding of the stellar environment.