'Into the Wild' is a Sean Penn film, and is based on a true story. Below is a synopsis of the film. Don't read it if you are planning on seeing the movie and do not know the ending as yet.
A young man leaves his middle class existence in pursuit of freedom from relationships and obligation. Giving up his home, family, all possessions but the few he carried on his back and donating all his savings to charity Christopher McCandless (Emile Hirsch) embarks on a journey throughout America. His eventual aim is to travel into Alaska, into the wild, to spend time with nature, with 'real' existence, away from the trappings of the modern world. In the 20 months leading up to his Great Alaskan Adventure his travels lead him on a path of self-discovery, to examine and appreciate the world around him and to reflect on and heal from his troubled childhood and parents' sordid and abusive relationship. When he reaches Alaska he finds he has been insufficiently prepared for the hardships to come. Despite making it through the winter his plan is ill-judged and prepares to return home in spring, only to find the stream he crossed in the snow has become an impassable raging torrent and that he is trapped. With no means of sustaining himself adequately he eventually starves to death in his so sought after isolation. Throughout his epic journey the people he meets both influence and are influenced by the person he is and bring him to the eventual and tragic realisation that "Happiness is only real when shared". (IMDb)
Emile Hirsch was brilliant as Christopher McCandless/Alex Supertramp, and I have read that he is working with Sean Penn on another movie at the moment.
There is an interesting piece written here by Jon Krakauer entitled "Death of an innocent: How Christopher McCandless lost his way in the wilds".