Nanna, also known as Sin or Suen, is the god of the moon in Mesopotamian mythology. His main symbol was the bull, as the crescent moon was often compared to cattle horns. Mesopotamian literature (for example the poems Herds of Nanna and A Cow of Sin) described him as the owner of large herds of cattle which he cared for himself. He was also regarded as a divine judge, and as such was invoked in oaths.
He was often regarded as a son of Enlil, and the myth Enlil and Ninil describes him as his firstborn and a brother of Nergal. However, it's possible in some areas and time periods he was himself the head deity, similar to how Dagan was the lead god and the "father of gods" like Enlil in the upper Euphrates area. His wife is Ningal, a goddess originally associated with reeds, while his most notable children are Inanna (Ishtar) and Utu (Shamash), representing the morning star and the sun. God lists sometimes referred to other gods as his children as well, for example Enlil's vizier Nuska.
The main centers of his cult in ancient Mesopotamia were Ur and Harran. The firstborn daughters of rulers were often appointed as high priestesses of Nanna in Ur.