Utnapishtim was an inhabitant of Anu. He carried out Qataka's execution, but became convinced she had somehow survived. He had a city-sized space ark constructed to save what he could of his world. Thus, he and his followers survived when Qataka destroyed Anu with a cobalt bomb. They pursued her to the Sol system and fought her, thinking her dead when her ship was destroyed. The ark was damaged in the flight and landed on Earth, in the Mashu mountains, far from the human habitations in Mesopotamia.
The travelling singer Avram found the entrance to the city-ship and learned the story of Utnapishtim and Ishtar. He understood it as a war between the gods which ended in a devastating flood. Avram later led Ace and Gilgamesh to Utnapishtim, where Ace told him of Qataka's survival as Ishtar. Utnapishtim helped Ace and the Seventh Doctor defeat her, uploading a computer virus into her cybernetic body and destroying it.
The Doctor gave Ishtar's technology to Utnapishtim, allowing him to repair his ship and leave Earth. He and his people colonised an uninhabited planet and their descendants were contacted by an Earth expedition in the 32nd century. (PROSE: Timewyrm: Genesys)