The story was made up by the robbers. to active voice

The robbers made up the story

gilgamesh is a hero by birth as the epic explains it. in the epic the birth is explained in the way which tells us that gilgamesh’s creation was made perfect by the contribution of various god and that signifies the goal in his life, which was to become a hero and save mankind. an example from the text says. "the glorious sun shamash bestowed upon him glory; adad the terrible god of storms bestowed upon him courage. the great gods perfected his magnificence beyond all others, terrible like the great wild bull. two thirds god they made him; one third man they made him." a man born with superhuman qualities and partly god is destined to be a hero.

the heroic deeds carried by him later in his life also prove the heroic character of gilgamesh. for example hi battle with the ultimate beast humbaba is a proof of his bravery and characteristic heroism. gilgamesh was warned about the beast as the text says about humbaba “whose roar is a flood, whose mouth is fire, whose breath is death". but with the superhuman strength gilgamesh did the job