Jad is a fictional solar god found in the works of Guy Gavriel Kay, including The Sarantine Mosaic series, The Lions of Al-Rassan and The Last Light of the Sun. In these books, all set in a fictional world loosely based on Europe during late antiquity and the early Middle Ages, Jad serves as an analog to God, as the focal point for an organized church (or group of churches) similar to the Roman Catholic and Eastern Orthodox churches. In addition to the mainstream church of Jad, there are a number of heretical and schismatic movements alluded to or described. The main division in the Jaddite faith stems from belief or disbelief in Heladikos, a fire-bearing celestial charioteer, and son of Jad. Heladikos is the Jaddite analogue of Jesus. Belief in Heladikos is outlawed as heretical by the time of Emperor Valerius II, an analogue of Justinian I. This is a marked difference from actual Christianity, which is formed around faith in the son of God.
In Kay's novels, the religion of Jad competes with the lunar religion of the Kindath, who are analogous to our world's Jews and the star-worshipping Asharites, who parallel our world's Muslims. The Jaddite faith is also opposed by various pagan cults, including those of the Erling (Viking) war god Ingavin, an analogue of Thor.