The Treasure of the Sierra Madre (1948)

Humphrey Bogart plays along side of John Huston's father, Walter Huston, in this dark movie about the lure that gold and money can hold over an otherwise decent man.
Bogart is down and out in Mexico when he meets up with two men who he ultimately decides to go off looking for gold with.  The Mexican hills are replete with both bandits and federales, either of whom are dangerous to the trio.  The most dangerous of all is their greed, however, especially for Bogart.  He develops a deep seated mistrust of his partners, and is willing to murder a man who comes upon them.  It is the age old story of money causing people to become a worse version of themselves, and while Bogart was warned of this before he sets out, he does not heed those words and it is ultimately his undoing.  Huston the father received a Best Supporting Actor Oscar and his son Best Director in the first Academy Award ceremony where father and son were both honored.  Well worth watching.