- "You dare to bring the warmth of life into my tomb?!"
- The Skeleton King greeting the Player, in a fashion similar to his speech in Diablo I.
The Skeleton King first appeared in the Wizard introduction trailer, greeting the Wizard and warning her to prepare herself to serve him for all eternity, much like the way he greeted the player that entered his tomb in Diablo I (at which the Wizard gave a confident grin). He was at this point present as a ghost giving orders to his numerous minions.
At the end of the trailer, where the Wizard stood before his throne, his ghost was seen stumbling backwards onto his skeletal body sitting on the throne, taking control of it and standing up with his huge mace held ready, laughing malevolently. He then staggered forward to the Wizard for battle.
In the playable demo, the Skeleton King was the end boss. Before entering the lowest level of the dungeon, a certain monster would drop the Skeleton King Crown near the entrance. Once the player entered the lowest level, he had to destroy two purple, glowing orbs. While active, these orbs occasionally summoned small groups of monsters to try to stop her. After destroying both orbs, the gate to the Skeleton King's throne room was opened. The player then entered the throne room and clicked on the throne to place the Crown on the dormant Skeleton King. This brought the King to life, beginning the final battle, which included groups of varying types of undead enemies.
As long as the King was alive, more groups of monsters would appear after the Wizard had killed the previous groups. As expected, the Skeleton King had a large amount of health as well as some incredibly powerful swipes with his multi-bladed heavy mace, which left a blurry image as it moved (even when it was stationary). However, he moved relatively slowly, making it possible to defeat him eventually with ranged weapons or spells while staying well away from his range, which was rather long despite being a melee attack (mostly due to his large size and the length of the weapon). Once the Skeleton King was defeated, any remaining monsters disappeared, and the King dropped several rare items. A few seconds later, text appeared on the screen saying "You won! Thanks for playing the Blizzcon 2008 demo." and the game returned to the class selection screen.
- "The power of the fallen star awakened me... and soon all will suffer, as I have suffered. Guards! Bring me his bones!" (First encounter, as the Skeleton King is seen chasing after Deckard Cain)
- "You dare to bring the warmth of life into my tomb?!" (Upon entering the Royal Crypts)
- "You will never defeat me!"