Who is Horatio? He’s described as a friend of Hamlet, a fellow student at Wittenberg. He seems to be Danish, since he speaks of the elder Hamlet as “our King” and of Danes as countrymen.
But he’s not from Elsinore: He’s unfamiliar with Danish court customs and with people such as Laertes and Osric, and he says he’s seen the King only once (and presumably recently, since he recalls that the King’s beard, like his ghost’s, was gray).
Marcellus and Barnardo, like Hamlet, seem to regard Horatio as a learned and trustworthy companion, but he’s not a close friend — Hamlet is surprised to see him and finds his absence from the university puzzling. Hamlet calls him a good friend, but Horatio calls himself Hamlet’s “poor servant ever.”
At the end of the play, Horatio promises to tell his friend’s story to the Norwegian Prince and “report [his] cause aright,” restoring Hamlet’s reputation and honoring his memory. University of Alberta political scientist Leon Harold Craig notes that this seems to mean that Horatio plans to reveal that Hamlet’s seemingly wayward behavior had been feigned. But “can Horatio plausibly explain why Hamlet should think it ‘meet / To put an antic disposition on’? Indeed, does Horatio even know himself?”
(Leon Harold Craig, Philosophy and the Puzzles of Hamlet, 2014.)