Marcellus is a guard at Elsinore, Barnardo’s companion on the midnight round.
With him, he witnesses the apparition of the ghost. He convinces Horatio to join them for the watch on the third night. He knows more about ghosts than Barnardo, and known to Hamlet. He risks physically restraining the latter from following the ghost, but later swears himself to silence over the whole matter of the haunting. He is concerned about the warlike preparations going on in Denmark, and feels that something is wrong in the world.