Albrecht
Prince Albrecht was the young son of King Leoric.
History
Diablo used Lazarus to take Albrecht down to the catacombs under Tristram Cathedral where the Lord of Terror's broken soulstone lay.
Diablo's spirit took control of Albrecht's young mind and fed on his terror. He then reformed him to match his own form.
The player character in Diablo I is sent down to find albrecht, but instead finds another boy sacrificed by Lazarus.
When Diablo was defeated, the unnamed warrior removed the soulstone from the Prince's forehead. His body transforms back to human form, and he dies.
The Warrior then tries to contain the demon, and bring him to the East where it can be killed once and for all, and sings the stone into his own forehead. He stays in Tristram a few days, but is later overtaken by Diablo's strong will and becomes the Wanderer.