In Shakespeare's Hamlet, a friend to both Prince Hamlet and the sentry Marcellus. A student in Wittenberg with a rather skeptic viewpoint, who refused to believe Marcellus and Bernardo saw a ghost (until he saw it himself) and later called Hamlet "desperate with imagination" for going to speak to the ghost. Hamlet disparages his "philosophy" when Horatio refers to all the ghost business as "wondrous strange."