Like the film noir detectives that came before him, Jake exhibits some of the common traits of a hard-boiled private investigator. He appreciates crass jokes, shows a willingness to get violent with both men and women who cause him trouble, and never lets physical threats scare him off a case. Unlike the traditional private eye, however, Jake can be disarmingly human. Though he isn’t scared by physical threats, he is susceptible to them and spends a good portion of the film wearing a large nose bandage. He starts the movie reluctant to take on a job he feels won’t satisfy a client. Unlike most Hollywood private eyes, Jake tends to be wrong more often than he is right, missing important information and putting clues together incorrectly.
The element that brings depth to Jake’s character is his odd inability to comprehend the larger picture. Nicholson subtly weaves in this shortcoming as his character develops, mainly through tantalizingly vague references to Chinatown, where the corrupt stay corrupt and everyone is supposed to look away. Jake was never very good at looking away, no matter how much trouble it caused him. Sadly, this also tends to cause trouble for other people, especially Evelyn Mulwray. Jake is a man perpetually in over his head.
In the classic tradition of film noir women, Faye Dunaway portrays Evelyn Mulwray as a person defined entirely by the secret she keeps. Her secret dictates the paced, careful precision with which she speaks, suggesting that every word is internally monitored before being let out into the world. It is also the reason Evelyn is so inwardly focused and distant and explains why she is so quick to take offense at even the most casual of personal comments. The moments when this shell cracks move the character beyond the genre cliché. Evelyn does not hide her secret as well as she thinks she does, and she occasionally lets her control slip. Tear-stained and lost, she seems desperate for a guide or protector in place of the father who betrayed her trust. At times, she reflects her fragile, hidden daughter Katherine.
During a brief window of time with Jake, Evelyn transforms into a woman who has had little chance to enjoy life. Through their encounters and brief romance she manages to reveal both quick thinking and a sense of humor. Evelyn craves the intimacy with Jake that she has often denied herself, both through sex and through wanting to hear more about his past. Ultimately, this urge is not strong enough to overcome the secret that dominates her life.
On the surface, Noah Cross appears to be a pleasant, jovial man. His speech is easy and untroubled, and his facial expressions remain open and friendly no matter what he’s saying. He has a knowing, faintly chauvinistic charm and a ready smile that manages to avoid any trace of psychosis or cruelty. As we discover, however, this harmless, appealing exterior renders the inner, sociopathic nature that it hides all the more frightening. Cross feels that neither society’s laws nor the basic laws of human decency should apply to him, and he treats human life with contempt. When asked about the rape of his daughter, he blames his actions on the depths of depravity people are capable of sinking to, but he gives the explanation with such utter calmness that it’s clear he doesn’t feel that he’s lowered himself at all. If Cross has a basic drive beyond self-interest, it is his need to control everything around him. From the town’s water supply to the profitable valley land to Evelyn’s and Katherine’s innocence, anything he feels might have value must be firmly in his possession.