Philosopher's Stone

The Philosopher's Stone is a substance that alchemists believed was able to turn base (impure) metals (such as lead) into pure gold. They thought it could also be used for rejuvenation (to become younger again) and to achieve immortality (to live forever).

The Alchymist, In Search of the Philosophers' Stone by Joseph Wright of Derby, 1771.

In popular culture

The first Harry Potter book is called Harry Potter and the Philosopher's Stone (Harry Potter and the Sorcerer's Stone in the United States).

The manga and anime series Fullmetal Alchemist.