The Epic of Gilgamesh is about a Sumerian king in Uruk, about 3000 BC. He was half god and when he was young he was not treating his subjects well initially. Gilgamesh loved hunting and sports.
The goddess Ishtar (Inanna) falls in love with him but he treats her badly. Later on the Gods create Enkidu, half human and half beast to defeat him due to his misbehaviors. They fight but they cannot beat one another and instead they became friends. Then the beast becomes more human and Gilgamesh is transformed into a better person.
Together they defeat Humbaba, the evil demon. The Gods decide to hurt Gilgamesh by killing Enkidu due to their disobediences and Gilgamesh is devastated and he goes underworld to seek immortality and to bring Enkidu back but he fails. He meets Utanapishtim who survived a flood just like Noah from the Bible.
Why is this story important?
It was the first written tale story. It was found in the 19th century and translated by George Smith (Assyriologist). It is universal and timeless because it talks about loyalty, friendship, fair play, immortality, love and weaknesses of humans. It makes us believe that the Great Deluge story of Noah in the Bible is historically true.
FURTHER READING : https://www.sparknotes.com