The Treasure of the Sierra Madre (1948)

Drifters Fred C Dobbs and Curtin share a cheap flophouse and meet Howard, a seemingly crazy old man who regales them with stories about prospecting for gold. Dobbs and Curtin cobble together what cash they can get a hold of, and along with Howard, plan a prospecting expedition. Dobbs promises that anything they dig up will be split three ways, but Howard doesn't believe them. As the gold is mined the men become increasingly distrustful, and soon turn against one other.