Since the objects of imitation are men in action, and these men must be either of a higher or lower type (for moral character mainly answers to these divisions, goodness and badness being the distinguishing marks of moral differences), it follows that we must represent men as either better than in real life, or as worse, or as they are.

[ἐπεὶ δὲ μιμοῦνται οἱ μιμούμενοι πράττοντας, ἀνάγκη δὲ τούτους ἢ σπουδαίους ἢ φαύλους εἶναι τὰ γὰρ ἤθη σχεδὸν ἀεὶ τούτοις ἀκολουθεῖ μόνοις, κακίᾳ γὰρ καὶ ἀρετῇ τὰ ἤθη διαφέρουσι πάντες, ἤτοι βελτίονας ἢ καθ᾽ ἡμᾶς ἢ χείρονας ἢ καὶ τοιούτους.]

Aristotle (384-322 BC) Greek philosopher

Poetics [Περὶ ποιητικῆς, De Poetica], ch. 2, sec. 1 / 1448a.1 (c. 335 BC) [tr. Butcher (1895)]
    (Source)

Original Greek. Alternate translations:

The objects the imitator represents are actions, with agents who are necessarily either good men or bad -- the diversities of human character being nearly always derivative from this primary distinction, since the line between virtue and vice is one dividing the whole of mankind. It follows, therefore, that the agents represented must be either above our own level of goodness, or beneath it, or just such as we are.
[tr. Bywater (1909)]

Inasmuch as those who portray persons -- who must be relatively good or bad, since thus only can character regularly be classified, for the difference between any characters is relative badness and goodness -- portray such as are better than, worse than, or on a level with ourselves.
[tr. Margoliouth (1911)]

Since living persons are the objects of representation, these must necessarily be either good men or inferior -- thus only are characters normally distinguished, since ethical differences depend upon vice and virtue -- that is to say either better than ourselves or worse or much what we are.
[tr. Fyfe (1932)]

Since those who represent represent people in action, these people are necessarily either good or inferior. For characters almost always follow from these [qualities] alone; everyone differs in character because of vice and virtue. So they are either (i) better than we are, or (ii) worse, or (iii) such [as we are].
[tr. Janko (1987), sec. 1.3]

Since those doing the imitating imitate people acting, and it is necessary that the latter be people either of serious moral stature or of a low sort (for states of character pretty much always follow these sorts alone, since all people differentiate states of character by vice and virtue), they imitate either those better than we are or worse, or else of our sort.
[tr. Sachs (2006)]

The thing that representative artists represent are the actions of people and if people are represented they are necessarily either superior or inferior, better or worse, than we are. (Differences in character you see derive from these categories, since it is by virtue and vice that people are ethically distinct from each other.)
[tr. Kenny (2013)]