.....Hrm. The closest thing in my current campaign is the old human wizard Martus (but wait, it gets more interesting a few lines later), whom the party met in the free city of Trelg (founded by hobgoblins, but built in human lands, so...). The party met strange old Martus when looking for someone to identify their magical loot, and perhaps buy some potions or other trinkets from. Martus had a small little tower in the Free Quarter of Trelg, where most of the wealthy folk live. He almost seemed to have expected them when they arrived, and welcomed them into his den for a bit of tea and to ask their purpose in coming to him. He had two apprentices sitting in the den at the time, Donovan and Haraad, whom he explained he had taken under his tutelage recently as they wished to learn the crafting of various magic items.
Martus wasn't exactly right in the head, though. He behaved a bit queerly, and had the look of a mad wizard or something, even though he was quite polite and had a posh little home, with his own well-stocked study and laboratories. It turned out that a few of the party members were invited to stay the night in his guest rooms while waiting for him to finish his Identify spells and such on their loot (8 hour casting time each go, y'know?). At some point, the familiar of the party's sorcerer got his attention and drew him over towards the door of Martus' home, where outside they found the scorched remains of what must of have been a would-be burglar, seeing as Martus hadn't even remembered to close the door earlier, and never locks it anyway. That would be because of the self-resetting lightning bolt magic traps he has inscribed along the inner rim of his doorway...... Rather casually, when the sorcerer fetched Martus over there, the old wizard just shrugged and said something along the lines of "well, there goes another burglar, I really should do something to fix that so I don't have to clean up remains any more......"
This was the first warning light to go off in the players' heads. The second was later in the night when the sorcerer was in the study and looking through the books, and noticed many of them on the restricted shelves as being warded. The third was when the party saw Martus in the morning before leaving, as the old wizard emerged rather haggard and ragged, looking like hell, and they had heard strange, muffled noises coming from his basement that night. The basement surrounded in a foot of stone a few inches of lead, with a big heavy door covered in wards. And the faint whiff of sulfur on Martus after he had emerged from the basement. The queer look in his eyes, and the very strong impression, from the books he had in the study and the kind of symbols and smells around the basement door, that Martus might very well, rather frequently even, be summoning and binding and dealing with fiends.
But he was such a very nice old man, and even left them with a small one-use talisman each, to summon a large earth elemental to serve them for a while in case they ever needed it....... Such a nice and generous old codger, y'know.........