Below are three central traits of Curley with a short explanation of how each trait appears in the novel and a supporting quote (note: exact wording can vary slightly by edition; check your copy of the book for page numbers).
1) Aggressive
Curley picks fights and looks for ways to prove himself against men larger than he is. His quick temper and readiness to attack are a constant source of tension on the ranch.
'What the hell you laughin' at?'
Context: Curley confronts Lennie (and others) with short, hostile challenges — this line, along with his physical attack on Lennie, shows how quickly he moves from suspicion to violence.
2) Jealous (especially of his wife)
Curley is possessive and jealous of his wife; he complains about other men looking at her and reacts with anger when he thinks a man has crossed a line.
'He wore a glove on his left hand, the glove was full of vaseline.'
Context: The glove is described as something Curley uses to pamper his hand for his wife. The detail emphasizes his possessiveness and his preoccupation with proving his claim on her, which fuels jealousy and tension with other men.
3) Insecure (compensates for his small size)
Curley is small and well aware of it; he constantly tries to assert dominance to mask his insecurity. His clothing and behavior are meant to show status and toughness.
'He wore high-heeled boots and spurs to prove he was not a laboring man.'
Context: Steinbeck’s physical description shows Curley using outward signs (boots, spurs, attitude) to compensate for his lack of physical stature and authority among the ranch hands. His aggression and jealousy are often ways of covering that insecurity.
Quick tip for essays: pair each trait with both a short quote and a brief explanation of the scene — then show how the trait affects other characters (for example, how Curley's aggression causes conflict with Lennie and raises tension across the ranch).