Diablo 1 Walkthrough -> King Leoric's Curse
Location: Level 3, Dungeon, The Skeleton's King Lair
Issued by: Ogden
After visiting the second level of the dungeons, you can try your luck with Ogden, the innkeeper, and receive a quest about the cursed king. Ogden will tell you a rather lengthy story about how they were once ruled by a noble and honest man who believed in light and justice. His name was Leoric, and the people loved him.
However, all that was good in the king then vanished, and he began to suffer from an incomprehensible madness. Toward the end of his earthly life, he completely lost his mind, and the kidnapping of his only son, Albrecht, drove Leoric to a frenzy of rage and murder. After his death, Leoric never found peace, and his spirit continues to terrorize and torment the townspeople of Tristram. You must free the soul of the cursed king.
On the third level of the dungeons is the square Tomb of the Skeleton King, with a single entrance on the south side. This is where you'll find yourself. The tomb consists of several sections: at the very beginning, upon entering, you'll find yourself in a hall with two small rooms. These rooms contain levers that will remove the bars blocking your path. Behind the bars, you'll encounter Leoric, the Skeleton King, surrounded by his minions.
Defeating them in a horde is quite difficult, so it's best to lure them to the entrance of the tomb and kill them there. The quest is made even more difficult by Leoric's ability to steal life from you and raise his skeletons from the dead.
It's very difficult to kill him in melee, and your best option is to use the Holy Bolt spell. Alternatively, you can try to lure Leoric to you before raising the second grate and kill him. In other words, use the Butcher's assassination tactic.
But this rarely happens; Leoric is often very far from the grate and won't always run up to you. Therefore, holy magic is the best option. After Leoric's death, the remaining skeletons will be much easier to kill, and the Tomb itself offers some good loot.
Reward: Upon death, Leoric will drop The Undead Crown, a magnificent headpiece for melee (at the cost of life steal).
Sources: diabloarea.net (by Kitty Venom), Kebooooo.
See also:
Diablo 1: Hellfire - Poisoned Well
Diablo 2 (Lord of Destruction) Complete Walkthrough
What's the best way to level up a paladin character in Diablo 2?