In the Epic of Gilgamesh, Ishtar sends the Bull of Heaven against Uruk after Gilgamesh rejects her.
Ishtar proposes marriage to Gilgamesh, but he refuses and lists the unhappy fates of her previous lovers. Angered by his rejection, she appeals to her father Anu and demands the Bull of Heaven. The beast is then released, causing death and destruction in Uruk.
Gilgamesh and Enkidu confront the bull together. Enkidu restrains it while Gilgamesh delivers the killing blow. Their victory increases their fame, but Enkidu’s insult toward Ishtar and the killing of the divine bull contribute to the gods’ decision that Enkidu must die.
The Bull of Heaven episode is distinct from the later fight with Humbaba. Both adventures bring fame to the heroes, yet the bull’s death is especially important because it directly precedes the punishment that separates Gilgamesh from his companion.