Lachdanan

Lachdanan himself will initiate this quest and can be found standing still on level fourteen. He is a Blood Knight, so your first instinct will likely be to attack him, which is futile. He'll ask you to get the Golden Elixir, which you can find in the center of a room on level fifteen. Return the Elixir to Lachdanan (don't worry, he won't attack), and he'll give you the Veil of Steel in exchange for it - and you'll give him his much-desired merciful death.