Spoiler alert! Don't read if you haven't completed the original Diablo from 1996.
At the end of the original Diablo, the hero shoves Diablo's soulstone into his or her forehead. That ending is identical for any hero choice. Is there a canonical "which hero it was" fact in Diablo II? e.g. do we know that it was a warrior that used the soulstone, and subsequently became the host for Diablo's new form?
From what I remember, and this forum thread agrees with me is that
This leaves the most likely outcome, the bulky Warrior became the canon Diablo in Diablo 2.
In Diablo 1 King Leorics son Prince Albrecht is kidnapped, driving the king mad, and used to give Diablo a human form by plunging the soul stone in to him, but he is not strong enough to let Diablo escape the dungeon. The warrior is his brother Prince Aidan and during his decent down in to the dungeon he is corrupted in to believing that the only way to control Diablo is to plunge the soul stone in to him self, but this is just a trick by Diablo to get a host that is strong enough for him to get out of the dungeon.
If you want more of the backstory i sugest watching this 3 part video: Pre Diablo 1, Diablo 1 and Diablo 2
Following this link you can see this part:
By spreading terror into the surrounding countryside, the Demon was able to attract many heroes who came to cleanse the land of evil. By the time the strongest of these heroes, Aidan, reached this goal, though, he had become fully influenced by the power of Diablo. In his twisted state, Aidan believed that the only way to fully control the Demon was to plunge Diablo's Soulstone into his own head. This, of course, was exactly what Diablo had planned, as the Demon now had an even stronger body to use to find his brothers and complete his ultimate plan... Diablo eventually possessed him and went to free his two brothers, Mephisto and Baal.
Besides that, there is:
- The Rogue who became Blood Raven
and
- The Sorcerer who became The Summoner
The warrior became the Dark Wanderer.
By the official game fiction though, the Warrior was the character who defeated Diablo at the end of the first game, and drove the soulstone into his head.
