Sol Invictus was the official sun god of the late Roman Empire and a later version of the god Sol. The emperor Aurelian revived his cult in AD 274 and promoted Sol Invictus as the chief god of the empire. The main festival dedicated to him was the Dies Natalis Solis Invicti on 25 December, the date of the winter solstice in the Roman calendar. From Aurelian onward, Sol was of supreme importance, and often appeared on imperial coinage. He was often shown wearing a sun crown and driving a horse-drawn chariot through the sky. His prominence lasted until the emperor Constantine I established Christianity as the Imperial religion. The last known inscription referring to Sol Invictus dates to AD 387, although there were enough devotees in the fifth century that the Christian theologian Augustine found it necessary to preach against them.

A solar deity or sun deity is a deity who represents the Sun or an aspect thereof. Such deities are usually associated with power and strength. Solar deities and Sun worship can be found throughout most of recorded history in various forms. The Sun is sometimes referred to by its Latin name Sol or by its Greek name Helios. The English word sun derives from Proto-Germanic *sunnǭ.