From the original Diablo to Diablo 3: Reaper of Souls, the Diablo series has had a long and serious, if totally grimdark, history, much of which is chronicled throughout the games—as well as through third party materials like novels, The Book of Cain, and a few other pieces of literary arcana.
Today, Blizzard unveiled a detailed retrospective of the Diablo franchise with the introduction of The Story of Diablo to its Game Guide. Within this ancient tome, you will find a spoiler-rich re-telling of all major events in the Diablo franchise up to Reaper of Souls.
You won’t have to read it to get good at the game, but it doesn’t hurt to know what you’re fighting for each time you throw a Blessed Shield at a pack of demons within the Nephalem Rift, or channel arcane energies as an Archon to destroy your foes.
You can reminisce and comment on your favorite moments from Sanctuary’s history within the Game Guide itself as long as you’re logged into the battle.net website. That’s kind of neat.
In case you missed it, here's our non-spoilery review of Diablo 3: Reaper of Souls.