Diablo 2 built upon its predecessor directly, continuing the story of the Dark Wanderer. The unnamed hero of the original game had placed the Soulstone, a magical stone created by the Horadrim to contain the power of Diablo and the Prime Evils, within themselves and commenced wandering. Players in Diablo 2 found themselves dealing with the aftereffects of the powerful item and all the denizens of hell and heaven that gathered to take advantage of its power Diablo IV Boosting.
In Diablo 3, players found themselves embroiled in the return of the forces of Hell in now New Tristram, again heeding the words of series mainstay Deckard Cain. Eventually, the players learn that they have been deceived by the farsighted Prime Evil, Diablo, but alongside a now-human Tyrael, they are able to defeat the embodiment of evil in Sanctuary. The Reaper of Souls DLC then saw heroes (alongside the addition of the Paladin class) dealing with a maddened Malthiel, the angel of death, and his attempt to turn the Soulstone into a weapon capable of harvesting all mortal souls.
Over its long lifespan, the story of Diablo has remained a very consistent piece of storytelling that dedicated fans have long enjoyed exploring. Voice memos and scattered notes throughout all of the games help to flesh out minor characters and major cosmology alike, magic items give descriptions that hint at exploits of famous adventurers, and the well-written dialogue of the main campaigns all work together to create a canon that is as deep as fans want. Casual players can get the best version of a succinct and compact story about good vs. evil, while those that want to delve deeper are treated to an expansive lore with thousands of years of history to explore.
Diablo 4 has already set the stage to eschew its traditional villains with the reveal in the original release trailer showing that the newest entry will be focused on Lilith, one of the demons that broke away from the Endless War to create Sanctuary. And with most of the other Prime and Lesser Evils seemingly defeated by the end of Diablo 3, the franchise stands in rarefied position to create new threats and to explore other characters that had previously been sidelined by the more immediate threats of a renegade angel and the devil himself buy Diablo 4 Boosting.