Dennis Miller
Tina Fey
Although mainly hydrogen, the composition of stars can vary quite a bit from star to star. It depends on what materials were around during the formation of the star that determines the composition, which would have been dictated by what had been there previously. Large stars with high masses have relatively short life spans, but towards the end of their life they enter into phases where heavier elements are used as fuel, producing heavier elements still. When the die, there is a supernova explosion. The heat and pressure during this time is so immense that the heaviest elements form through fusion. The mixtures of elements left over from such events will spread out and become part of new solar systems, when new stars beginning to form. The different concentrations of elements will give us stars of varying compositions.