"To be or not to be," thought Hamlet. "That is the question." Hamlet spends the entirety of the play imprisoned in his own incessant negative thoughts. Whether obsessing over his recently deceased father and king, whining about his mother's choice of a second husband, or contemplating his own suicide, Hamlet exhibits many of the classic symptoms of depression.
The narrator in John Irving's classic prep-school epic "A Prayer for Owen Meany" is about as depressed an individual as you'll encounter in modern literature. He loses his mother at the hands of his best and only childhood friend in a fluke accident and essentially never recovers. He loses the ability to make simple decisions and to take even the most necessary actions. He spins and spins over the same depressed thoughts from the time he's 10 right through the novel's end when he's in his 50s. He lives his entire life as passively as "Joseph," Irving's reference to Jesus' earthly non-father, who plays no role of consequence in the birth and life of Jesus.
The troubled teen from Salinger's classic "A Catcher in the Rye," Holden Caulfield, lives in the dark night of his mind. His depression takes all manner of forms in the novel, from violent outbreaks, screaming fits, and flunking out of school after school to the more physiological symptoms of constant headaches, nausea, and even some fainting spells.
While the beautiful, rich Daisy Buchanan may be the girl of the dashing Jay Gatsby's dreams, she manages to manifest several of the most common symptoms of depression throughout Fitzgerald's novel. First, she is the woman who apparently has everything from the mansion on the water to the all-American athlete husband, and yet she is chronically bored and disappointed. She drinks to drown her feelings, cheats on her husband constantly but won't leave him, and is prone to taciturn moods and periods of complete passivity.