Which king established religious customs in ancient Rome?

Numa Pompilius is the king credited with establishing religious customs in ancient Rome. He was the second king, following Romulus, and his reign is often associated with the introduction of various religious practices and institutions that helped shape Roman religion and law. Numa is known for creating the office of the pontifex maximus, enhancing the role of priests in civic life, and introducing a calendar that included religious festivals.

His contributions were significant in promoting the idea that the Romans had a unique relationship with their gods, which was central to Roman identity and culture. Numa’s reforms emphasized the importance of religious observance and moral conduct, laying the groundwork for the religious structure that would influence Rome for centuries.

The other choices, while important figures in Roman history, did not primarily focus on the establishment of religious customs. Romulus was more focused on the founding of the city and its initial governance. Tarquinius Superbus is known for his tyranny and the eventual downfall of the monarchy, and Augustus was focused on political reform and the consolidation of power in the empire rather than the establishment of new religious customs.