Marcellus asks, "Who hath relieved you?" "What, has this thing appear'd again to-night?" and "Is it not like the King?" (I.i).
Marcellus is a guard of the court who arrives outside the castle with Horatio, a friend of Prince Hamlet. They are on duty and discuss a ghost that has appeared to them. Since Horatio is a scholar and only believes what he is able to see, he has come to see the ghost himself. They are not sure if the ghost is a warning or an evil spirit there to pull them into Hell. Since Horatio knows Latin, it is believed that if the ghost is evil, he will be able to perform an exorcism.
When the ghost appears, it looks very much like the late King of Denmark, and it is wearing the King's armor. The ghost does not speak. At the end of the scene Horatio decides that he must go tell Prince Hamlet of the sighting. This act foreshadows Horatio's loyalty to Prince Hamlet.