Though he seems like a pretty minor character for most of the book—mostly because he is—Joseph—or should we say, Zafenat Paneh-ah—ends up having a surprising transformation. In his childhood, he's Dinah's best friend and her most-liked brother. But after the massacre of Shechem, he's sold into slavery and becomes a whole different person.
Joseph ends up landing in prison, then gets out of prison, and then he becomes the king's right-hand man. This dude is like Andy Dufresneon steroids. But when he does come into power, he turns into a nasty man. When Dinah scolds him, she says: "Let me be free of this place, for it is a tomb to me. Seeing you is like stepping into the past where my sorrow lies. And now because of you, I lose all hope of my son" (3.4.118).
If Joseph were a benevolent man, maybe Dinah would have pity. But instead, she only sees her troubled past and her son's troubled future. It's a coincidence that Re-mose becomes Joseph's apprentice—and this coincidence gives Dinah even more grief. Basically, Joseph is a bad teacher and a bad brother.
Re-mose echoes Dinah's notion, calling Joseph "[a] murderer and a liar. How dare you claim innocence in this abomination? Perhaps you raised no sword yourself, but you did nothing to stop them" (3.4.94).
Now, Joseph's not evil. It's not like he's the one who goes on the bloody rampage in Shechem, for one thing. But Joseph doesn't help his beloved sister, and because of that, we can't help but dislike him a bit. He turns his back on Dinah, and because of this, Joseph becomes something of a traitor in our eyes, despite his unfortunate past.