Lachdanan
Lachdanan is a quest that takes place on level thirteen of the dungeon in Diablo I, and begins when the player speaks to the Unique Steel Lord of the same name. He informs the player that he was once one of King Leoric's Royal Guard, but as Diablo corrupted the King, he cursed the knights who were not there to protect him from the evil to serve him in darkness for eternity. All the Royal Guard turned into evil mockeries of their former selves, save one: Lochdanan. He tells you of an elixir that could free him from Diablo's curse, located on the fifteenth level of the dungeon (usually in a heavily-guarded pentagram). Upon returning the elixir to Lachdanan, he thanks the player, who then recieves the Veil of Steel, a Unique Full Helmet.
Veil of steel