In the Epic of Gilgamesh, what immortal man survived the great flood?

In the Epic of Gilgamesh, the immortal man who survived the great flood was Utnapishtim.

Utnapishtim was a king of Shuruppak who received a warning from the god Ea, also called Enki, that the gods would send a catastrophic flood. He built a large boat, brought aboard his family, craftsmen, animals, and provisions, and survived while the rest of humanity was destroyed. After the waters receded, he offered a sacrifice to the gods.

The god Enlil was initially angered that anyone had survived, but Utnapishtim and his wife were ultimately granted eternal life. In Tablet XI of the Standard Babylonian Epic of Gilgamesh, Utnapishtim tells this story to Gilgamesh, who has come seeking a way to defeat death. Utnapishtim tests him by challenging him to remain awake, a trial Gilgamesh fails.

The same flood hero appears under other names in related Mesopotamian traditions: Ziusudra in Sumerian sources and Atrahasis in an earlier Akkadian story. Gilgamesh is the seeker, not the flood survivor; Shamash is the sun god, and Enkidu is Gilgamesh's friend.