Sam Spade is a no-nonsense private investigator with an eye for the ladies. He is a heavy drinker and smoker, with a violent temper. Very strong physically, he uses his fists instead of a gun to intimidate his enemies. Spade is greedy and tries to get as much money as he can but he is also honorable and capable of doing the right thing. Spade also has a strong sexual side. Women are drawn to him, and he takes advantage of this. His relationships, however, seem superficial, and he is a loner.
Brigid O'Shaughnessy is both beautiful and deadly. She is a femme fatale who attracts men with her sexuality and then manipulates and deceives them to get what she wants. A habitual liar, she tells many falsehoods over the course of the story, such as hiding her true identity with aliases like Miss Wonderly or Miss Leblanc. Brigid partners with different men to find the falcon. But she is deceitful and greedy and uses the men to her own selfish advantage. It remains unclear whether her relationship with Spade is based on love, opportunism, or a combination of the two.
Casper Gutman is a grossly fat, corrupt man who is consumed with his obsession to find the Maltese falcon statuette and sell it for millions of dollars. His manner is relaxed and genial, but behind his casual facade he is actually greedy, corrupt, sadistic, and extremely violent. Gutman will stop at nothing, including murder, to get what he wants.
Effie Perine is very loyal and obedient to Sam Spade, acting as his secretary. She does whatever is asked of her and is honest and compassionate. On many occasions she serves as Spade's sort of moral compass, questioning his treatment of the women in his life and encouraging him to do the right thing. She may be attracted to Spade. He calls her names like "darling" and "honey," and they have a close bond, although not a romantic or sexual one. Because Spade can only see women sexually, his behavior toward Effie is often flirtatious and provocative.
Joel Cairo is hired by Gutman to find the Maltese falcon. He is deceitful and greedy and can be violent. He gets into arguments with Spade and Brigid as well as threatening them. Cairo is also suspected of being a homosexual, and others mock his effeminate manner and overwhelming perfume.
Wilmer Cook is the boy trailing Spade on Gutman's orders. He gets angry very quickly and always has his hands thrust into his pockets, gripping guns. Wilmer is a killer who seems to have no remorse. He murders Thursby, Jacobi, and in the end, Gutman. It is suggested that he may also be a homosexual and possibly involved with Cairo. He and Spade have some very violent encounters with each other.