This question popped into my head when I did a brief Write or Die session: what do I know about the Soul Stones in the Diablo ‘verse? In the original Diablo, your character hacks and slashes his or her way through a dozen-plus floors and kills Big D, only to find out that he’d possessed the body of the young prince who’d been kidnapped. Slaying the demon killed the boy, but from one perspective, it could be seen as a mercy kill.
The final cinematic of Diablo delivers the punch that your character drives Diablo’s red rock into their own forehead — thus setting up for the sequel, Diablo 2. In Diablo 2, you play as a different adventurer who’s following in the wake of chaos and destruction that result from Diablo’s hero on his journey eastward. The cinematic cut-scenes we get between acts give us the idea that the Lord of Terror has possessed the mind and body of the warrior.
The next Soul Stone we encounter is the one we get for slaying Mephisto, Lord of Hatred, at the conclusion of Act 3. It’s blue, and we carry it around with us throughout Act 4, until we reach the quest in Hell’s Forge, where we destroy it, presumably with Mephisto inside. At the conclusion of Act 4, we defeat the Lord of Terror for a second time, and the cinematic that plays informs us that his Soul Stone was destroyed at the forge, but one of the three “brothers” escaped: Baal.
Baal is seen recovering his Soul Stone from the dude in the cut scene, and we’re set up for the expansion, Lord of Destruction, where we chase down and defeat the last of the three “Prime Evils.” When we finally confront Baal, he’s gone and corrupted a massive “World Stone,” that’s at the top of a mountain, and this is supposed to be a bad thing. We’re treated to a cinematic of one of our angelic buddies shattering the World Stone to prevent its corruption from … spreading or something. It’s cool, but what does it mean?