Samuel Spade operates a private investigation firm in San Francisco. He maintains a cynical, emotionally detached exterior and refuses to cooperate openly with the police. Driven by an internal code of ethics, he projects physical confidence and reacts to threats with calm calculation rather than panic.

Brigid is an attractive, highly secretive woman who travels to San Francisco seeking protection. She initially claims to be looking for her runaway sister but soon admits this is a lie to secure Spade's services. She uses a performance of helpless innocence to secure assistance from the men around her, continuously concealing her true motives regarding the black bird.

Joel Cairo is a neat, heavily perfumed man carrying a Greek passport who comes to San Francisco searching for an extremely valuable artifact. His mannerisms are fastidious and precise, yet he quickly proves willing to resort to violence by pulling a gun on Spade during their first meeting. He shares a historically strained connection with Brigid.

Casper Gutman is an immensely wealthy and heavily overweight man obsessed with tracing the history and location of the Maltese falcon. He enjoys the sound of his own voice and treats business negotiations like a refined game, offering Spade a drink and a cigar before demanding information. He relies on hired men to handle physical confrontations while he directs operations from his luxury suite.

Effie Perine is Spade's dependable secretary. She possesses a boyish face and provides Spade with unwavering loyalty and a stable presence in his chaotic work environment. She manages the office efficiently and often pushes back when Spade acts callously, acting as his sole trusted confidant in San Francisco.

Wilmer Cook is a young, undersized man working as Casper Gutman's personal gunman. He aggressively shadows Spade through the streets of San Francisco. He overcompensates for his physical size by openly carrying two large guns in his overcoat pockets and reacting with immediate hostility to any perceived insult.

Miles Archer is Samuel Spade's partner at their private detective agency. He eagerly volunteers to personally tail Floyd Thursby after noticing the large sum of money in Brigid's purse. His early murder in a dark San Francisco alley sets the entire chain of investigations in motion.

Iva Archer is Miles's widow. She is secretly involved in a romantic relationship with Spade, a situation that makes the police highly suspicious of Spade's motives following Miles's murder. She is emotionally volatile, frequently demanding Spade's attention while harboring deep jealousy regarding his female clients.

Lieutenant Dundy is an aggressive San Francisco police officer investigating the recent homicides. He strongly suspects Spade of foul play and regularly pushes for an arrest. He refuses to accept Spade's evasive answers and uses direct confrontation to try and force a confession.

Tom Polhaus is a police officer and colleague of Dundy. He is more even-tempered than his partner and attempts to maintain a cordial, working relationship with Spade. He acts as a buffer between Dundy's aggressive interrogation tactics and Spade's stubborn refusal to cooperate.

Floyd Thursby is a criminal with a violent history as a hired gunman for a prominent gambler. Brigid hires Spade and Archer specifically to track his movements, claiming she fears for her safety in his presence. He is heavily armed and highly paranoid about being followed.