Bernardo is a soldier on watch with Horatio at the beginning of the play. He sees the ghost of King Hamlet and alerts Horatio to it.
Francisco:
Francisco is a soldier on watch with Bernardo at the beginning of the play. He is replaced by Bernardo and leaves the stage.
Marcellus:
Marcellus is an officer who comes with Horatio and Bernardo to investigate the appearance of the ghost. He is the first to speak to the ghost and tries to get it to speak, but it does not respond.
King Hamlet:
King Hamlet is the deceased king of Denmark and the father of Prince Hamlet. He appears as a ghost to Horatio, Bernardo, and Marcellus and tells them that he was murdered by his brother, Claudius, who is now king.