The Triumvirate is a group consisting of a Hero of Strength, a Hero of Skill and a Hero of Will. These should not be confused with the Albionite ones of Fable II. The Triumvirate lived in a land far to the east of Albion a long time ago, though after the Fable events, since the Hero of Skill uses a gun. They were an invincible force only stoppable by death. They created a sword, a gun and a gauntlet to preserve their might.
In Bowerstone Castle's library in Fable III there are four statues describing the Triumvirate. If you read all four statues in the correct order a door opens in the library leading to a somewhat mundane treasure.
The Hero of Strength[]
The Hero of Strength was, unlike Hammer, a man. He could mow down entire armies with his sword.
The Hero of Skill[]
The Hero of Skill was the best shooter the world has ever seen, though Reaver disputes this.
The Hero of Will[]
The Hero of Will was perhaps the most powerful of the Triumvirate. He was powerful in his ability to control the elements and using them for powerful spells.