|“||Many adventurers tried and failed to slay the Skeleton King. It was left to Leoric's eldest son Aidan to finally kill the monster his father had become.||„|
|~ Deckard Chain about Aidan whom was forced to killed his undead father.|
The Dark Wanderer is the Warrior from Diablo who has been possessed by the demon Diablo, the very demon he sought to contain within himself.
After finally engaging Diablo in a duel in the depths of the hell beneath Tristram, the Warrior defeated and killed the Prime Evil. However, by this time he had been thoroughly corrupted by the demon's influence, and was led to believe the only way he could contain the Lord of Terror was by placing Diablo's foul soul within his own body, inserting the Soulstone in his forehead.
The Dark Wanderer is established in background materials for Diablo II as the warrior from Diablo I. In the Book of Cain, he is given the name "Aidan" and is revealed to be the eldest son of King Leoric. Upon saving Deckard Cain in the Diablo III beta, Deckard is found in New Tristram with the dialogue option "The Skeleton King". During this dialogue Deckard Cain reveals information about the warrior.
Aidan was part of what would become the ruling family of Khanduras, accompanying his father King Leoric, his mother Asylla, his brother Albrecht, and their court from Kehjistan to the Western land. Their court was set up in an abandoned monastery at Tristram and over time, Leoric gained the respect of the people.
Aidan was tutored by Deckard Cain. With the first game established the fact that Albrecht was Leoric and Asylla's only son, Aidan's identity as the prince and Albrecht's brother is somewhat retconned or rather, his true identity as the prince is kept the secret by his family, though he would never revealed it to anyone since the fight against Diablo.
Over time, however, Leoric's mood became increasingly unpredictable and erratic, his rule became extremely brutal and oppressive, and in the throes of such madness, he sent his army against the neighboring kingdom of Westmarch. Aidan was among the soldiers sent into battle. What he doesn't know was the source of his father's corruption was Diablo's corrupted soulstone that kept deep under Tristan with Archbishop Lazarus as conduit of the said corruption.
The war against Westmarch was a disaster, the armies of Khanduras being cut to shreds. Aidan survived however, and made his way back to Tristram, already suffering under whatever evil was plaguing it and drawing numerous adventurers to the town because of it (that, and gold).
By the time Aidan arrived, things had gotten even worse. His father had been struck down by the knight Lachdanan, Albrecht was missing and his kingdom was in shambles.
Aidan vowed to rescue his brother and banish whatever power had gripped the kingdom, though Cain urged caution. He warned Aidan of the demons beneath the cathedral and of the undead, how he might have to face those he once knew. Cain also pointed out that there were others who could aid him and as such he was joined by a Rogue named Moreina , who was part of the Sisters of the Sightless Eye and a Vizjerei Sorcerer, Jazreth.