The Defiler is a quest given to the player as soon as he or she enters the Festering Nest. This quest involves finding The Defiler on the fourth floor of the Festering Nest and killing her. The monster will then drop the Cathedral Map, which is needed in the Grave Matters quest and to gain access to the Demon Crypts.

Initiation:

"We have long lain dormant, and the time to awaken has come. After our long sleep, we are filled with great hunger. Soon, now, we shall feed..."

Upon entering level 3 of the Festering Nest:

"These lands shall be defiled, and our brood shall overrun the fields that men call home. Our tendrils shall envelop this world, and we will feast on the flesh of its denizens. Man shall become our chattel and sustenance."

Diablo and Hellfire quests
Diablo I quests
Anvil of Fury • Archbishop Lazarus • Arkaine's Valor • Black Mushroom • The Butcher • Chamber of Bone • Diablo • Gharbad the Weak • Halls of the Blind • Lachdanan • Magic Rock • Ogden's Sign • Poisoned Water • Skeleton King • Warlord of Blood • Zhar the Mad
Hellfire quests
The Defiler • Farmer's Orchard • Grave Matters • The Jersey's Jersey • Little Girl • Na-Krul • Reconstructed Note