The god associated with rain and fertility in ancient Mesopotamian beliefs is **Enlil**. He was considered a vital deity, often revered as the lord of the wind and associated with the essential agricultural cycles that depended on rainfall. Enlil's role in mythology was crucial, as he was believed to control the weather and ensure the sustenance of life. His worship was central to various city-states, underscoring the deep connection between the environment and spiritual practices of the time.