Using the Very Large Telescope in Chile, astronomers have identifed a number of stars with masses thought to range from 150 to as much as 300 times the mass of our Sun. Fun quote from the press release:
Within [star cluster] R136, only four stars weighed more than 150 solar masses at birth, yet they account for nearly half of the wind and radiation power of the entire cluster, comprising approximately 100 000 stars in total.
Stars this gigantic are believed to end their life in an explosion so intense it destroys the star entirely, leaving nothing behind but an expanding debris cloud, from which other stars and planets (and even life) can form.