Gugalanna

, the Bull of Heaven (天の牡牛), was the greatest of Divine Beasts in Mesopotamian legends.

Background
Gugalanna released by the god after Ishtar clung to her father in tears to obtain revenge on Gilgamesh for his insults and refusing to become her husband. It was a disaster of extreme magnitude that was clad in storms. It brought about a flood and dark clouds that covered the world, causing a seven-year famine and destruction to occur on earth. It was a beast none could stand against, bringing the downfall of Uruk. Gilgamesh and Enkidu stood against it and repelled it splendidly, binding it with his chains and destroying it with his weapon. The clouds faded and the land was saved from the flood, but Ishtar plead for their deaths due to one with a human body killing a beast of the gods being a sin. Enkidu was subsequently killed afterward because he could not resist the gods.

Development
Gugalanna's was designed by PFALZ. He first utilized the design in his doujin Gugalanna - The Bull of Heaven in 2012. The design was first officially utilized in a Type-Moon work in Fate/Grand Order in 2017.