Throughout the course of the Epic of Gilgamesh, the title character must overcome a number of enemies.
In one instance, Gilgamesh must overcome someone who becomes his friend, namely Enkidu. Regarding this conflict, perhaps one could say that Gilgamesh must resolve the challenges that the forces of the wilderness pose to the city and civilization. After all, Enkidu is a being from the wilds, whereas Gilgamesh is associated with the city. The friendship between Gilgamesh and Enkidu might represent resolution of the conflict between city and countryside.
After resolving this conflict, Gilgamesh and Enkidu set out to defeat Humbaba, Guardian of the Forest. Frequently in mythology, the forest is a place of mystery and evil. Perhaps Gilgamesh's defeat of Humbaba indicates his ability to eliminate that mystery and evil. The fact that Gilgamesh also cuts down the cedar forest may also represent his ability to civilize this mysterious zone.
In Tablet 6, Gilgamesh's battle with the Bull of Heaven is a result of his refusal to give in to the goddess Ishtar's sexual advances. In this encounter, Gilgamesh's struggle with heavenly powers has both positive and negative consequences. He gains fame, but at the same time loses his friend and is hit with larger questions about life and death.
The death of Enkido sends Gilgamesh's journey off in a different direction. Now, he becomes concerned with these issues of life and death. Ultimately, he has to face his own mortality as he loses the plant Utanapishtim tells him about:
A snake smelled the fragrance of the plant,
silently came up and carried off the plant.
(Maureen Gallery Kovacs translation)