One of the hardest bosses in the game Dark souls. Ususally killed before his parter, Executioner Smough, due to his extreme awesomeness after Smough is killed. He is quick and agile and will attack you when you least expect it. After Smough dies first, he absorbs his souls, grows to twice his usual size and starts stabbing you with a giant electric spear. If Ornstein is killed first then Smough will pulverize his dead body with his hammer, which will then become electric due to the AWESOMENESS of Ornsteins soul.
Person 1: We're dead
Person 2: But we just killed Smough!
Person 1: Exactly.
Person 2: But now we just have to kill Ornstein!
Person 1: EXACTLY
Person 1: no
(they carry on playing)
Person 2: Oh.
Person 1: Yeah. He is too awesome for us.
Person 2: No wonder he's called Ornstein the Dragonslayer. If he can kill dragons, we must be as easy as flies!