In the Epic of Gilgamesh, the flood survivor is named Utnapishtim.
Utnapishtim appears in the epic’s Flood narrative when Gilgamesh seeks the secret of immortality. Utnapishtim tells him that the god Ea warned him to build a great boat and preserve life before a catastrophic flood. The Mesopotamian story shares broad motifs with Genesis, including a chosen survivor, a boat, animals, birds, and the eventual settling of the waters.
The name Atrahasis belongs to another Mesopotamian flood tradition, preserved in the earlier Epic of Atrahasis. In that story, the survivor is usually called Atrahasis, while the Gilgamesh version uses Utnapishtim. This is why both names can appear in comparisons with Noah without being interchangeable answers.
Utnapishtim is not Noah under a different biblical name. He is a character in a separate ancient Mesopotamian literary tradition, though the stories are often studied together as flood narratives.