The ghost of King Hamlet appears in the first scene of Shakespeare's Hamlet and continues to be a presence and driving force in the entirety of the play, even when he is only seen by his son. The Ghost materializes in the night, showing himself first to the watchmen at Elsinore (1.1) and later to his son Hamlet (1.4). King Hamlet is seen armed "cap-a-pÃÂ©," in a suit of armor similar to that which he might have worn "When he the ambitious Norway combated" (1.1.70-1) The Ghost wears his beaver and visor up so he is easily recognized as the late King by those who see him. The plot of Hamlet revolves around the message the late King delivers to his son: he tells of his murder at the hands of Claudius and urges Hamlet to avenge the death of his father. The manifestation of the Ghost is a central aspect of the play, and the appearance of the King armed from head to toe is a symbol that can be read many ways.
The watchmen, Horatio, and Hamlet discuss the costume of the Ghost, indicating that the armor is significant enough for its appearance to be emphasized in the opening of the play, suggesting that Shakespeare considered the armor significant to the script.
The King appears in armor as he would have looked in battle, as Marcellus and Horatio observe in 1.1.68-74: Marcellus: Is it not like the king?