Once he was friends with Strongheart the paladin, but then he turned to evil when exposed to the Heartstone! This magic item drew out his cruel nature.
He also has close relationships with several women, allying with Skylla, an evil wizard. He is loved by a cleric named Raven who was once good herself, and hated by the cleric Mercion.
His steed is nightmare, a nightmare. He is a member of the Horned Society, a nation based on the adoration of foul outsiders. Iuz invaded their lands during the Greyhawk wars, and most of the order was destroyed. However the leader was reborn as a devil, known as the Unnameable Hierarch, who rose to power only through the efforts of a ruthless fighter, named Warduke.
"Warduke is the soldier's bogeyman, the opponent seasoned veterans least hope to see when the battlefield fog clears and reveals the faces of the enemy. Tavern tales suggest Warduke's hand in the destruction of several complete adventuring Parties. . . Warduke works alone, preferring to challenge enemies of the Horned society in direct combat. He cares nothing for decorum, often assaulting his quarry as they emerge battered and tired after a dungeon crawl or prior battle. He speaks with a raspy, otherworldly voice and possesses a morbid sense of humor. He takes pleasure in brutality and tenaciously hounds his enemies."
From AC1 - The Shady Dragon Inn:
"WARDUKE especially hates STRONGHEART, who he feels wastes his time protecting the weak and helpless. 'A true fighter,' WARDUKE feels, 'makes himself rich and powerful by the strength of his sword arm. He takes what he can — if you would keep your possessions, kill those who seek to take them.' He calls his sword 'Nightwind.'"
His stats from Heartstone: