The Collaborative International Dictionary of English v.0.48:

Gilgamesh \Gilgamesh\, Gilgamish \Gilgamish\prop. n.
   1. (Sumerian mythology) A legendary king of Sumeria and the
      hero of famous Sumerian and Babylonian epics.
      [WordNet 1.5]

   2. The Epic of Gilgamesh, a long Babylonian epic written in
      cuneiform in the Sumerian language on clay tablets. Early
      versions of the written story date from 2000 B. C.; it is
      probably the first written story still in existence. A
      longer version was written in the Akkadian language, on 12
      clay tablets found at Nineveh in the ruins of the library
      of Ashurbanipal, king of Assyria from 669 to 633 B. C. The
      story depicted the life and heroic deeds of the legendary
      Gilgamesh, apparently derived from stories about a real
      king of ancient Mesopotamia who lived around 2700 B. C.
      The story includes a tale of a great flood, which has some
      parallels to the biblical story of the flood survived by
      Noah. The Nineveh tablets name the author of that version
      of the story, a Shin-eqi-unninni.
      [PJC]

   Note: The entire text may be found in:
         The Epic of Gilgamesh
         Translated by Maureen Gallery Kovacs
         (Stanford: Stanford University Press, 1990)
         and
         Gilgamesh
         Translated by John Maier and John Gardner
         (New York: Vintage Press, 1981)