Vidian

"There you are. Don't tell me you never suspected I was more than what I seemed. It was the only way I could get close to you. And now, we're about to get much closer..."

- Vidian to the Nephalem

Vidian, Lord of Envy was a demon who dwelt in the Temple of the Firstborn with his followers.

The Eternal Conflict
"Vidian was always an...unusual demon. I only beheld him once, as he would seldom obey the will of his master, Azmodan. But on that occasion, he was only too ready to bring disorder to the angelic host. When he first appeared, we did not know of his insidious threat, and focused our attacks on his mightier brethren. It did not take long before the angels themselves were beginning to turn on each other, and question their leaders. By the time we figured out what had happened, the battle was lost, and it was too late."

- Tyrael

Vidian was once one of Azmodan's Sin Lieutenants. Unlike Azmodan's other lieutenants, Vidian seldom obeyed the commands of his master, though during those times that he did, he had a talent for sowing discord and disorder among the Heavenly Host, which cost the angels at least one battle during the course of the Eternal Conflict.

Blood of the Nephalem
"I've seen so many heroes like you. It's always more fun to fight alongside a friend, don't you think?"

- "Daivin" to the Nephalem

At some point after Diablo's fall, Vidian took up residence in the Temple of the Firstborn. At some point after the defeat of Malthael, Vidian's presence, new or otherwise, became noted, as the Horadrim learnt of something stirring beneath the Shrouded Moors. A newly formed Blood Cult took up residence in the temple, and at Vidian's direction, they twisted the flesh of mortals and bent creatures to their ill will. Their particular prey were the newly emergent nephalem, whose blood and power Vidian and the cult desired for themselves, and who they ensnared at times of vulnerability. Vidian personally led more than one adventurer into the temple's depths to die.

In what would be his last attempt at beguilement, Vidian encountered the Nephalem in the Shrouded Moors, to whom he posed as a human named "Daivin the Adventurer." He offered to join the hero(es) as they made their way through the moors. After the Nephalem destroyed the Blood Statue, Daivin commented that they may have brought bad luck upon themselves.

Upon entering an excavation above the temple, Daivin was imprisoned in a cage of bone by Theodosius Jordan &mdash; one of the cultists who had taken up residence in the temple. The Nephalem slew the cultist, but Daivin was apparently killed and torn apart by the cage. In what was apparently his last moments, Daivin asked the Nephalem to not fail him.

At the bottom of the temple, "Daivin" appeared to the Nephalem a final time. He taunted his foe(s) before assuming his true form of Vidian, Lord of Envy. He engaged the Nephalem in battle, while summoning fellow demons to his side. As the fight progressed, he mocked the Nephalem's allegiance to Tyrael. It came to naught, as Vidian was slain.

In-game
Vidian appears in the Adventure Mode of Diablo III, where he takes on two forms. His first is as "Daivin the Adventurer" (Daivin, unsurprisingly, being the anagram of Vidian) who functions as an NPC follower until The Excavation.

He later appears as a boss at the end of the Temple of the Firstborn, within the Sanctum of Blood area (accessed from Level 2). The fight will occur in a square arena without any objects or obstacles.

Vidian is a greatly empowered Reborn:
 * He retains their iconic ability to teleport at will.
 * His energy barrage is very powerful, and unless the character is moving, he can kill them in one cast.
 * At 50% Life or lower, he will periodically summons a pack of Favorites of Vidian, overgrown Disciples.
 * Every 25% Life lost, he will summon a swarm of Blood Vermin.
 * At 66% and 33% Life, Vidian will split, creating two illusions of himself. These illusions are very fragile, but will deal full damage with their energy barrages.
 * At 50% Life and lower, Vidian will enrage, dealing much higher damage. Visually, he will emanate a red glow and change into a much more monstrous form.

Vidian is also present as a Rift Guardian: Vesalius is his empowered version that focuses on damaging abilities rather than minions.

Quotes

 * "You are not the first to die here."
 * "Let me see you bleed..."
 * "I am like no other demon!"
 * "So much power...you could rule the Burning Hells instead of playing servant to a fallen angel."

Trivia

 * Vidian's name is possibly derived from the Latin word "invidia", meaning "envy".
 * Like Baal (whose corruption manifested as scarabs) and Belial (butterflies and botflies), Vidian seems to be linked to Tomb Roaches as his symbolic insects.