The Philosopher's Stone is a fabled legendary substance that is said to be able to turn metals into gold. Also it is said to provide an elixir of life which could allow the user to become immortal. This object has been considered the final goal for alchemy. The legend says that Albertus Magnus discovered the stone and then passed it on to his student Thomas Aquinas during the 13th century.
One of the people who is said to have dedicated a good amount of time on the search for the perfect formula to create the philosopher's stone is 14th century alchemist Nicolas Flamel. In Harry Potter and the Philosopher's Stone Flamel (who really existed) makes an appearance as the only person who ever succeeded in creating the philosopher's stone and he managed to live until 1992, thanks to the powers of the stone.
Philippus Paracelsus - a 16th century alchemist - believed that a single element could be used to create any other one. This theory was based on the fact that some minerals contained trace amounts of gold, it was of his thinking that this proved that such an element exsisted.
The Philosopher's Stone has appeared in a number of video games; one of the more notable being Harry Potter and the Philosopher's Stone.