Who is the play Hamlet about?

Hamlet is a play, a tragedy, written by William Shakespeare in 1599. The play's main character, Prince Hamlet of Denmark, is a young man beset with many problems. His father, King Hamlet, has been murdered by his own brother, Claudius. Claudius has taken over the throne and married King Hamlet's widow, Gertrude. The ghost of Prince Hamlet's father, the murdered king, appears to his son and urges him to avenge his murder.
Throughout the play, Hamlet struggles with many problems. He isn't entirely certain that the visit from his father's ghost was real, so he questions his sanity. He suspects, for good reason, that his classmates Rosencrantz and Guildenstern have been dispatched by Claudius to spy on him. He wonders if his mother is complicit in his father's murder. He suspects that his girlfriend, Ophelia, might also be working against him. He tests Claudius to see if he will implicate himself in the murder of Hamlet's father. Hamlet even considers whether he should kill himself, but he worries about what might happen to him after death.
In the end, Hamlet, Ophelia, Claudius, Gertrude, Laertes, and Polonius all die, and Hamlet's sole loyal friend, Horatio, offers his tribute to his fallen friend.