One reason that Gilgamesh is such an epic hero would reside in his mere birth. Gilgamesh was described as ""Two thirds they made him god and one third man." This enables him to be perceived as more than a man, but not quite an immortal. The next best thing would be an epic hero, someone who is capable of great feats and inspiring actions. In this, one sees how Gilgamesh is an epic hero. Feats such as defeating Humbaba and the Bull of Heaven immortalize him. These actions are what contributes to Gilgamesh's condition of being an epic hero.
At the same time, Gilgamesh's condition is one in which he comes to understand truths about what it means to be human. He experiences pain, misunderstanding, and the all too construction of mortality. Gilgamesh is such an epic hero for while he does that which reminds us of the greatest of immortals, his grasp of what it means to be human is where he acquires a knowledge that enables us to relate to him. His stature does not subsume his human nature, and it is this element where he becomes such an epic hero.
Epic heroes possess very specific characteristics which define them as epic heroes. Epic heroes must possess the following characteristics:
-Complete long and dangerous journeys (which typically contains a descent into the underworld).
-Desire to gain fame and fortune.
-Compete in epic battles which illustrate his (or her) aristeria and arete (greatness and supremacy in battle).
-Understanding that death can come at any time.
In regards to The Epic of Gilgamesh, Gilgamesh possesses all of the characteristics defined above. He goes on a journey to find Utnapishtim, enters into the underworld (where he passes through twelve levels of darkness), wishes to possess the answer to an eternal question (secret to life) and gain fame, competes epic battles (Humbaba, Bull of Heaven, and Enkidu), and earns immortality in order to overcome the possibility of death coming.