Prince Albrecht was the young son of King Leoric. Diablo attempted to claim the King's body, but was not strong enough to fully take possession. The Demon required a host, simple and innocent, and thus found Albrecht to be fitting.
Albrecht was captured by the traitorous Archbishop Lazarus and was taken all the way down into the depths of the Catacombs. Diablo's shattered Soulstone was driven into Albrecht's forehead, and the Demon's vile spirit entered his body and eventually assumed his true form.
A group of heroes- a Vizjerei sorcerer, Blood Raven the Rogue captain, and Albrecht's own brother, Prince Aidan- entered the darkened Monastery in an attempt to find and rescue the Prince. Lazarus was encountered and defeated at the Unholy Altar, but the adventurer only found a different child, sacrificed by Lazarus as an offering.
Unwilling to give up hope, the heroes sought out, encountered, and eventually vanquished the Lord of Terror himself. Diablo let out a tortured scream of death, which went all the way up to the mortal realm, shattering the windows of the Tristram Cathedral. Kneeling down beside the defeated Prime Evil, Aidan used a small blade to remove the Soulstone from Diablo's forehead. Diablo's body transformed back into that of Prince Albrecht, who then gasped his final breaths.