Hi, he sought Utnapishtim, who is sort of an equivalent to Moses, both of them had to build a boat in order to save themselves from the great flood that gods sent them. Utnapishtim was awarded immortality for being loyal to gods, and Gilgamesh is obsessed with the idea of eternal life, thus he seeks Utnapishtim and gods (primarily Enlil) to become immortal as well.
