Both Gilgamesh and Enkidu are heroic (willing to perform challenging deeds) and extremely strong. The two share the exact same lineage/parentage.
These heroes differ in important areas too, as Gilgamesh is the bolder of the two. He is bold to the point of being brash and he enjoys the power he holds over others (at least he does at the opening of the epic story).
Enkidu is a helper and protector. He is a figure of sympathy, helping the animals escape traps and later confronting Gilgamesh to save the city from his hubris and greed. Enkidu is less adventurous than Gilgamesh.