Short answers, pulled from the story.
Gilgamesh was a king of the Sumerian city-state of Uruk who was posthumously deified and became the protagonist of the oldest surviving long epic poem. Scholar Stephanie Dalley places his lifetime between 2800 and 2500 BC, within the Early Dynastic Period of Mesopotamia roughly spanning 2900 to 2350 BC.
The standard Akkadian version of the Epic of Gilgamesh was composed by a scribe named Sîn-lēqi-unninni, probably during the Middle Babylonian Period around 1600 to 1155 BC. The most complete surviving copy, recorded on twelve clay tablets dating to the seventh century BC, was found in the Library of Ashurbanipal at Nineveh.
The Akkadian text was first discovered in 1849 by the English archaeologist Austen Henry Layard in the Library of Ashurbanipal at Nineveh. The first translation was produced in the early 1870s by George Smith, a scholar at the British Museum, who published the flood story from Tablet XI in 1880 under the title The Chaldean Account of Genesis.
Classics scholar Barry B. Powell argues Greeks were exposed to Mesopotamian traditions through their connections to ancient Near Eastern civilizations. German classicist Walter Burkert identified a direct parallel between the rejection of Ishtar in Tablet VI of the Gilgamesh epic and a scene in Book V of the Iliad, and Powell notes that the Odyssey shares multiple structural elements with the epic, including a hero who visits the Underworld, encounters an enchantress, and loses his chance at immortality.
Utnapishtim, the sole human survivor of the Great Flood, challenged Gilgamesh to stay awake as a test of worthiness for immortality. Gilgamesh failed and slept for seven days. Utnapishtim then told him of a rejuvenating herb at the bottom of the sea, but after Gilgamesh retrieved it a snake stole it from the shore, and Gilgamesh returned to Uruk empty-handed.
The flood story in Tablet XI bore strong similarities to the flood narrative in the Hebrew Bible, triggering intense scholarly and religious debate in the late nineteenth and early twentieth centuries. In January 1902, German Assyriologist Friedrich Delitzsch lectured before the Kaiser at the Sing-Akademie zu Berlin arguing that Genesis copied the Gilgamesh flood narrative directly, generating thousands of critical articles and pamphlets and eventually costing him the Kaiser's support.