In Shakespeare's "Hamlet," Horatio, the close friend who is willing to die beside Hamlet is extremely astute and referred to as "the scholar." He is originally skeptical of the ghost because he believes it to be a "fantasy" (I,i,23). So, the others beg him to accompany them on their watch that he may see the apparition and judge. When Horatio sees the ghost, he agrees that it resembles King Hamlet, and he tells the others that he is filled with "fear and wonder" (I,i,54). Nevertheless, Horatio is braver than the others and addresses the ghost, but it refuses to respond. Horatio tells the others that he might not have believed in this spectre had he not seen it himself. Also, he notices that this ghost is clothed in armor resembling that which he wore when he defeated Fortinbras of Norway. Because of this, Horatio fears that young Fortinbras will challenge Denmark, entering the country in battle; he fears a strange eruption in the state:
In what particular thought to work I know not;/But in the gross and scope of my opinion,/This bodes some strange eruption to our state.
In this exposition to Shakespeare's "Hamlet," Horatio is clearly established as a strong friend to Hamlet as the others have him see the ghost so that he will call Hamlet to its witness. Horatio is also intuitive as he has a sense of foreboding.
Horatio is a man of science and learning (science was often called "philosophy" in Shakespeare's time -- as when Hamlet says "There are more things in heaven and earth, Horatio,/Than are dreamt of in your philosophy" I.v.186-7). He has been a student with Hamlet in Wittenberg ("And what make you from Wittenberg, Horatio?— " I.ii.168) and is particularly scholarly. Through his studies he has become sceptical of occult phenomena, though he witnesses it twice with his own eyes. He counsels patience and logic to Hamlet throughout the play, and tries to convince him not to take rash action based on the advice of what appeared to be a ghost. ("These are but wild and whirling words, my lord." I.v.146)
Horatio represents reason and cool-headedness in this play; he is practically the only major character who does. Claudius, Gertrude, Ophelia, Polonius, and even the absent Laertes each have a kind of overriding passion or madness which affects their reason. Everyone else is too involved in the plot; Horatio stands alone as the sole unaffected -- and coolly reasonable -- courtier. Hamlet would have done well to listen to Horatio's scepticism, and have taken his advice.