Dragonslayer Ornstein is a powerful knight of Lord Gwyn who was among the last guardians of the Anor Londo cathedral, home of the Gods. Many theories surround Ornstein, as he is the last of the surviving knights of Gwyn.
When initially encountered, he defends the cathedral alongside Executioner Smough, a cannibalistic executioner who vied to be among the knights of Gwyn.
It has been confirmed that the Old Dragonslayer boss in Dark Souls II is indeed Ornstein, although he appears corrupted by the Abyss, and uses dark powers.
Eventually, Ornstein left the Grand Cathedral in search of the Nameless King for an unknown reason. He found him, as his weapon and armor are found in Archdragon Peak.
Many theories surround Ornstein. One popular theory is that the Ornstein you find in Anor Londo is in fact an illusion created by Gwyndolin. Another is that Ornstein is merely undead, explaining why he has survived far longer than any of his compatriots, and allowing him to survive his encounter with The Chosen Undead, simply returning after death. A theory for Dark Souls II is that, knowing that time is convoluted in Lordran and thus unpredictable, it could potentially be a displaced Ornstein or even an alternative, as nothing is impossible in theory. Finally, a major theory in the third installment of the game is that Ornstein indeed found the Nameless King, and became his great dragon.
Powers and Stats
Tier: At least 6-B
Name: Dragonslayer Ornstein, Old Dragonslayer
Origin: Dark Souls
Age: Thousands of years
Classification: Dragon Slayer
Powers and Abilities: Superhuman Physical Characteristics, Electricity Manipulation, Spear Mastery, Darkness Manipulation, Immortality (Types 1 and possibly 7), Absorption, Soul Manipulation, Magic, Size Manipulation
Striking Strength: Class ZJ
Stamina: Very High, as with many of the Gods Ornstein can do battle against immortal dragons, defends the Cathedral for many years before leaving
Range: Several meters with spear, potentially far higher via magic
Weaknesses: None notable