Troilus and Cressida.
Cressida and Troilus.
Who’s the protagonist of this play?
Well, I guess that depends on your definition of protagonist…
If you feel the character who’s on stage the most is the protagonist, then Troilus is your guy. Troilus appears in more scenes than any other character. But what does he actually do? He’s in love with Cressida, but Pandarus has to broker their meeting. He goes to the Greek camp, but can only watch and comment upon Cressida’s betrayal. He vows revenge on Diomedes, but the Greek’s still breathing then the play is done.
If you feel that the hero, the good guy, is the protagonist, then Aeneas is probably your best bet. No one else in the play is postive from start to finish. Troilus? Whiny at the beginning, broken and depressed at the end. Ulysses? A schemer. Achilles? Not even. Hector? Well, Hector sounds great until his penultimate scene: he finds a Greek soldier whose armor he likes, and he chases the poor soldier down and kills him for it. Not heroic. And don’t even think of “false” Cressida. Aeneas, he‘s a good guy, out for what’s best for his army, looking after Troilus’ emotional state. But realistically speaking, Aeneas is nowhere near to being a major character in the play (let alone THE main character).
If you feel that the character for whom we have a rooting interest is the protagonist, then the protagonist is Troilus? I put a question mark there because, really do we root for him? Do we actually care for any of these characters? (And don’t even say you’re a Thersites fan…)
If you think the character with the greatest motivation, the one who wants to achieve something, is the protagonist, then your man is Pandarus. From the beginning, he’s trying to bring together our titular couple. At the mid-point in the play, he gets them together. At almost EXACTLY the three-quarter point of the play, he suffers “the major setback” of having his couple torn apart (it is here that Diomedes takes possession of Cressida); and he can’t even bare to watch it (he leaves the scene nearly 80 lines earlier after saying, “Where are my tears? Rain, to lay this wind, or my heart will be blown up by the root!” [IV.iv.52-3]). And at play’s end, he’s broken but still has a purpose. He needs to say goodbye to us: we’ll die of his “diseases” (V.x.56), his legacy to us, his “brethren and sisters” (V.x.51).
Don’t buy it? How about this: at 153, Pandarus has the most speeches of any character in the play (more than Cressida  and Troilus ).
He’s not on stage the most times, but he’s there when it matters most to our title couple.
Pandarus may not be the good guy (he’s no more than an “ill requited” [V.x.38] bawd); his name will devolve into a synonym for “brokers-between” (III.ii.198), pimps.
We may not root for him.
He doesn’t speak in the lofty language of the (seeming) major characters (in fact, he has the most degraded diction in the play).
But he’s us, we are him, and–deal with it–Pandarus is our protagonist.
This is one messed up play. Problematic.