Illidan Stormrage was, at one point, a nigh-godly sorcerer with an unusual amount of skill. He quickly turned to the profession of demon hunting, allowing his power to grow exponentially faster. He would eventually turn to assist Sargeras and was imprisoned for his efforts, only to be killed much later.
However, after his death, Illidan's true intentions were revealed- he had planned to turn on the Burning Legion and Sargeras, and save Azeroth from the infinite demonic horde.
Powers and Stats
Tier: At least High 6-A, possibly 5-C
Name: Illidan Stormrage, The Betrayer, Lord of Outland, Lord of the Naga, King of the Shadows
Age: Unknown, at least ten thousand years old
Classification: Demon Hunter
Powers and Abilities: Superhuman Physical Characteristics, Hellfire Manipulation, Fel Manipulation, Magic, Necromancy, Flight, Enhanced Senses, Immortality (Type 1 and 9, cannot be truly killed as his demonic soul simply returns to the Twisting Nether until a suitable host can be found), Summoning, Aura, Energy Projection, Blade Mastery, Martial Arts, Attack Reflection, Can Sense Magic and Powerful Beings, Adaptation, Regeneration (At least Low), Tattoos Increase Arcane Power, Absorption of Power, Rage Power, Status Effect Inducement, Soul Manipulation, Shadow Manipulation, Darkness Manipulation, Fear Manipulation, Illusion Creation, Possession, likely far more
Attack Potency: At least Multi-Continent level (Capable of battling Arthas for an extended amount of time, Casually created another Well of Eternity, the former version of which could do this), possibly Moon level (Most speculations state that Illidan was in fact superior in strength to Arthas, and that the latter had to muster excess power from Frostmourne in order to defeat him, is by and large considered an equal to Arthas)
Lifting Strength: Unknown
Striking Strength: Unknown (Comparable to Arthas, should an exact quantifier be found for these)
Durability: At least Moon level (Survived many wounds taken from a max AP Arthas, to the point where Arthas had to dig into Frostmourne's reserves to be able to fight back)
Stamina: Superhuman (Can fight Arthas to a standstill)
Range: Up to hundreds of meters with magic abilities
Standard Equipment: Blades of Azzinoth, Skull of Gul'Dan, Blindfold, Eye of Sargeras
Intelligence: At least Extraordinary Genius, superior mage to almost all sorcers of the time (considered an equal to the most skilled)