The elder priest is a terrifying figure with a paralyzing gaze, clerical spellcasting abilities, and a distinctive melee attack which destroys your worn armor. In addition, the priest is covetous and will try to steal the Amulet, the invocation artifacts, and your quest artifact. If destroyed, the priest will quickly revive like a Rider.
The elder priest is generated with a blessed +3 quarterstaff, blessed +3 cloak of magic resistance, potions of full healing and extra healing, and a leather drum and wooden flute.
Unlike in vanilla, the Wizard of Yendor is capable of killing the Elder Priest if you can lure him in (such as with the guaranteed 12 turn appearence after you perform the invocation).
Given its encyclopedia entry, the elder priest who guards the Amulet of Yendor in dNetHack is probably the high priest that appears in H. P. Lovecraft's The Dream-Quest of Unknown Kadath. The high priest is a mysterious but disturbing figure shrouded in yellow silk, which sits alone in a temple on the Plateau of Leng in Lovecraft's Dreamlands, and communicates with visitors by playing an ivory flute.
Commentators on Lovecraft's writings have speculated that this being is either a servant of Nyarlathotep, or an avatar of the "crawling chaos" itself.
From Leng, where rocky peaks climb bleak and bare
Under cold stars obscure to human sight,
There shoots at dusk a single beam of light
Whose far blue rays make shepherds whine in prayer.
They say (though none has been there) that it comes
Out of a pharos in a tower of stone,
Where the last Elder One lives on alone,
Talking to Chaos with the beat of drums.
The Thing, they whisper, wears a silken mask
Of yellow, whose queer folds appear to hide
A face not of this earth, though none dares ask
Just what those features are, which bulge inside.
Many, in man's first youth, sought out that glow,
But what they found, no one will ever know.
[ H. P. Lovecraft, Fungi from Yuggoth XXVII. ]