Act I of Shakespearean dramas present the exposition, or background, information of the play. Hamlet is no different. In this act, the reader meets all the key characters, learns the background information necessary to understand the play and understands the origins of the central conflict. In Act I, the reader learns that three guards have witnessed the late King Hamlet's ghost wandering the castle outposts dressed in his war gear. The guards call Hamlet's friend Horatio to confirm the sighting.
Hamlet is introduced as a depressed young man who is trying to reconcile his father's sudden death and his mother's hasty remarriage to his father's brother, Claudius. Claudius has taken the crown and is badgering Hamlet to stop mourning. He also is attempting to quell a hostile takeover by Fortinbras of Norway.
Hamlet's girlfriend, Ophelia, is bidding her brother farewell as he returns to college while their father, Polonius gives him some advice. He then turns to Ophelia and demands to know the details of her relationship with Hamlet. He ends the talk by forbidding her to see him because he is worried she might get pregnant.
Horatio tells the nearly suicidal Hamlet that his father's ghost has been sighted. Hamlet seeks out and talks to the ghost. The ghost tells him that it was his own brother, Claudius that killed him and orders Hamlet to get revenge. Hamlet concocts a plan to get his revenge on Claudius.