Clavicus Vile is the Daedric Prince of wishes and trickery. He is responsible for the loss of Vivec's power and the primary antagonist of the The Elder Scrolls Online: Morrowind questline on Vvardenfell.
War Chief Helushk will give you a key to the Odious Chapel and instruct you to offer the Vacant Daedric Soul Totem to the blood fountain of Clavicus Vile. After doing so, the Prince will communicate to you through a red mist called the Voice of Clavicus Vile and say "You bear a gift? How thoughtful! But I can't accept it without providing one of my own." You will begin to kneel in pain under Vile's influence and he will say "I know! I'll share the same gift I gave Stillrise Village. Now you can play skeever-wicket with your own skull! Hahaha!" and give you the "Curse of Stillrise," turning you into a skeleton.
At the Vile Terminus, the Voice will appear again and say "You've felt the true splendor of my gift to Stillrise Village. What gift have you for them, I wonder?" at the hallway to the Fires of Destruction and Ice of Statis. If you have told Shaman Chirah you sided with him, Vile will say "Preserve their existence or end it forever. Which will it be? Probably the boring one." after. His dialogue afterwards will vary on what you choose to do with the Soul Gem Array:
Array is destroyed (Fires of Destruction): "Heartless oaf! You'd destroy everyone in Stilrise Village, despite the ones who clearly wish to go on? All to end pain and sickness they can no longer feel? How delicious."
Regardless of each choice, he will then say "Now begone."