Ra's al Ghul (which translates as The Demon's Head) is a DC Comics villain and a recurring opponent of Batman. He is one of few villains that knows Batman's secret identity and he is also the only villain in Batman's rogues gallery whose crimes are commited on a global scale rather then just being confined to Gotham City. Ra's is the leader of a worldwide terrorist organization whose goal is to achieve a new environmental balance in the world; but however noble his goals may be, he attempts to achieve them through mass murder and even outright genocide.
Ra's al Ghul has lived for many centuries thanks to the Lazarus Pits, cauldrons of alchemical waters with potent rejuvenating properties. As long as he has access to one of these pits, he is essentially immortal.