The nameless hero is the protagonist of the Gothic franchise and is more of an avatar for the player in the world of Gothic rather than a well developed hero. In Gothic 1, the nameless hero is sentenced to a life of labor in the Valley of Mines and is given a letter to give to the Fire Mages from the outside world.
Though his crimes remain unclear, the nameless hero never argues his innocence and thus seeks to make his new life in the Valley of Mines. When the player chooses which camp to join (among the Sect Camp, the Old Camp, or the New Camp) ultimately the nameless hero is thrown into a conflict involving the Sleeper and his entrance into the Gothic world from beyond. He prevails, but at the cost of his own life.
In Gothic 2 the nameless hero is revived, only to be thrown into another struggle involving the elemental dragons, especially the great Undead Dragon. By Gothic 3, the nameless hero is prepared for the ultimate climax of the Gothic world. He can side with Beliar and the rule of all things dark and fearful, Innos, the god of goodness and honor, or serve his ally Xardas in ruling out all godly struggles throughout the world of Gothic.
In Forsaken Gods, it is assumed that the nameless hero sided with Xardas and must return once again, somewhat begrugingly, to save humanity from itself. By the end of the trilogy, the nameless hero has come from a lowly criminal to the most powerful man in the world of Gothic. He was sworn to be Rhobar III, king of Myrtana.
In Gothic 4 action is set 10 years later. The Nameless Hero (known now as King Rhobar III) is an evil king. We are playing another character, known as "Second Nameless Hero". His task is to unmake him a king, kill him, convince him that he shouldn't be evil, or ignore him.