This quest is activated near the end of the Arcane Sanctuary quest when you meet him.
NPC Quest Dialog
Quest Activation Dialog
The Summoner: *Tortured Laugh*
Atma: "You always seem to find the worst trouble. I don't know how you handle it."
Deckard Cain: "The appearance of the mage you describe sounds like one I met back in Tristram. Many Vizjerei came to fight against Diablo, the Lord of Terror. Perhaps, this is one of them. You know, fate seems to have frowned upon all of the heroes who confronted that terrible Evil. Take care or the same may happen to you."
Drognan: "Yes... The man you speak of sounds like the mage who came here many months ago. He claimed to have fought Diablo in the passages beneath Tristram. No doubt the fool wandered into Horazon's Sanctuary and lost whatever was left of his ravaged mind. He is beyond salvation. It is possible that the fool has been possessed by the spirit of Horazon. If that's true, then you'd better put an end to his tortured existence. Once done, I believe the demons who were summoned and imprisoned within the Sanctuary will cease to exist as well."
Elzix: "Ugh... Crazy mages give me the creeps. Just kill him and get on with your business."
Fara: "Hmmm... That doesn't sound like Horazon. I'll agree that he may have gone mad, but from what you tell me, I don't think that's the case. Talk to Drognan... he may know more than I."
Geglash: "So! Horazon's crazy, eh? I'd be surprised if he wasn't. All those centuries without ale would drive anyone to drink... but then you couldn't drink. And that would drive you to drink... Hah?... What was the question?"
Greiz: "That guy really talks like that? Sounds like either Horazon has gone stir-crazy or that's some impostor."
Jerhyn: "The man you describe is probably not Horazon. He sounds like the very mage who came around here a while ago. He was very curious about this palace and seemed especially interested in the seal on the passageway in the cellar. He left shortly after that. I wonder how he got down there? The seal was never broken... That mage spoke a great deal to Drognan. Why don't you ask him about it?"
Lysander: "Ah, yes. I remember. There was a... fellow around here many months ago who asked almost as many questions about Horazon as you. So... He discovered enough to assume Horazon's place in the Arcane Sanctuary, huh? What a fool!"
Meshif: "Ah, yes. As a ship captain I am well aware of the phenomenon of a false Horazon. Sorry, just a little joke."
Warriv: "There's nothing more dreadful than a powerful being driven by a frayed mind."
Atma: "You're more the hero than I could have dreamed. Perhaps, there is hope for us after all."
Deckard Cain: "I hope that this false Summoner found peace in death. Unfortunately, it is more likely that he will be dragged down into Hell by the demons he was bound to. Let this be a lesson to you... Demonic magic is a quick path, but its powers are seductive and deadly."
Drognan: "Larger forces are moving inexorably towards us. You must now make haste to the Tombs."
Elzix: "You make me long for the days of glory. When I had both hands, both eyes and more of a foot..."
Fara: "I feel no pity for that would-be Summoner. His terrible ambition for demonic power was his undoing. You merely hastened the inevitable."
Geglash: "The way I see it... Well, it's all pretty blurry."
Greiz: "So, Horazon's been dead for some time. I take it you at least found what you were looking for."
Jerhyn: "The demonic force that was emanating from the corrupted Sanctuary has dissipated. I thank you greatly for your help. Now, we can look to rebuilding our lives. All will be for nothing, though, if you do not stop the greater Evil which is rapidly gaining ground."
Lysander: "Huhhh... Such is always the fate of those who meddle with evil."
Meshif: "Well! You've got what you're after. Now get a move on before it's too late."
Warriv: "I guess you'll be heading to the Tombs now? I hear that they're in the deepest desert regions."
Character Quest Dialogue
Amazon: "Good riddance, freak!"
Assassin: "Horazon, your decoy is dead."
Barbarian: "Oh, I hate staining my hands with the blood of foul sorcerers."
Druid: "Finally. Now I can leave this twisted nightmare."
Necromancer: "He was not Horazon, he was a diluted fool who got too close to true power."
Paladin: "Rest in peace tortured soul."
Sorceress: "That couldn't have been Horazon. Poor wretch."