Taxi Driver is an intense portrayal of a man slowly being driven mad by his isolation and loneliness.  Although Travis Bickle (Robert DeNiro) lives in NY, the largest city in the world, his inability to construct and maintain relationships with other people has led to insomnia and progressively towards violent insanity.  He seems to have only one friend, the Wizard (Peter Boyle), a fellow taxi driver with whom he maintains an awkwardly trusting relationship, but even that contact with another person is largely superficial and deeply flawed.  On his downward spiral, he meets Betsy (Cybill Shepard), a woman whose company gives him hope to become "like other people".  Ultimately, though, his warped personality drives her away and sends him deeper into his own personal hell.