God is the Creator of the Universe and of humanity, the Alpha and the Omega. In the Abrahamic monotheistic traditions (which include Judaism, Christianity, and Islam), He is seen as the force of infinite power, knowledge, and benevolence in the universe, although among them, the Abrahamic religions do conceptualize God differently. Moreover, belief in a single deity may found in non-Abrahamic religions, including certain Hindu movements, Sikhism, and in the Baha-i faith.
While a variety of characters in the works of Harry Turtledove may or may not believe in God, and may invoke God, this article should focus on those works in which God is a direct character, the belief in God is a critical plot point, or alternate history characters' concept of God is significantly different than in OTL.
God in "Before the Beginning"
Despite misconceived notions to the contrary among other great religions, God favored Judaism. For this reason, He allowed Jewish-French detective Jacob Dreyfus to speak with Him when Dreyfus looked through the time-viewer to before the Big Bang, though He had killed non-Jews who attempted the same thing. Once God's true preferences became widely known, nearly everyone in the world converted to Judaism in short order.
God in Crosstime Traffic
God in Gunpowder Empire
Christianity regarded its God (who shared his being with Jesus) as the sole deity in the universe. However, Christians were a weak minority in the Roman Empire. While the Empire generally tolerated their religion, it regarded their God as merely one of many deities officially recognized by the state.
God in In High Places
The Second Revelation, the religion which dominated a Europe just picking itself up from the Great Black Deaths, taught that God had two sons, Jesus and Henri, the latter being the more important of the two.
God in Worldwar
The Race found it virtually impossible to grasp the idea of a completely immaterial, disembodied God, believed in by several Tosevite religions. The only Divine beings recognised by the only religion known to the Race - Emperor-worship - were exalted members of the Race itself, the present Emperor and the Spirits of Emperors Past. By analogy, the God which Tosevites believed in had to be one of the Tosevites themselves. Moreover, at least one of the main Tosevite religions - Christianity, especially its Catholic version - did indeed portray God as a Tosevite, which could be readily seen in any Catholic church. The fact that Islam and Judaism were completely opposed to such a depiction of God was too much of a subtle and confusing nuance to truly register with the Race.
Members of the Race found the idea of the whole universe having been created by a "giant Big Ugly" ("God") ludicrous. This led many Christian, Muslim, and Jewish humans to resist Race rule in parts of Europe, Africa, South America and especially the Middle East. Other believers, such as Moishe Russie, Mordechai Anielewicz, and Pope Pius XII, were willing to cooperate with the heathen Lizards in worldly matters, and the Race did not intend to make belief in God rather than the Spirits of Emperors Past prohibitive in the granting of citizenship to humans.
God in "Islands in the Sea"
Chrisitan and Muslim delegations argued in the courts of pagan monarchs over which faith enjoyed God's preference, though each acknowledged that the other worshiped the same God, Who was the only deity in the universe. The main dispute was over they ways of worship and the nature of God.
God in "Occupation Duty"
Most people in the world were polytheists or henotheists, such as the Philistinians who worshipped the pantheon of Dagon, and the Arabs who worshiped The Four, while the Buddhists of the Middle Kingdom and the Turks of Babylonia practiced variants of a non-theistic religion. Everyone generally clung to one's own gods but did not bear particular hostility towards anyone else's gods, unless the tribes were at war.
Among the perpetually restive Moabites, however, a disturbing new movement was growing. While the Moabites had long worshiped Chemosh as head of their own pantheon, there was a trend among certain zealots to declare that not only was Chemosh superior to other gods such as Dagon of the Philistines (chief enemy of Moab), but that Chemosh was the only true god in the Universe, while Dagon and others were either demons or did not exist at all. Proponents of this belief depicted Chemosh as a fatherly old man with a full white beard.
God opposed the attempts of Aztec gods to begin a Third Sorcerous War.
God in Thessalonica
The Christians of Thessalonica invoked God's intercession for the protection of their city from the Slavs and Avars. God worked many miracles on their behalf throughout the siege, and when the city was attacked directly by Perun and other Slavic gods, God manifested Himself as a shield of light protecting the city and its defenders from the pernicious enemy deities.
The Jews of Thessalonica also invoked their own God to help them. And though the Jewish God did not visibly manifest Himself, he did effectively protect his worshipers from various supernatural attacks made against the city by the Slav and Avar magicians. Thus, the attack by a Slavic water elemental whose avatars burst out from various cisterns in the city was not manifested in the Jewish quarter. Similarly, when an Avar fire goddess was invoked for a spell putting off fires in the city, this did not affect the Jews. George the shoemaker did not bother himself with the vexed theological question of whether the Christian God and the Jewish God were two manifestations of the same or two separate beings; he was glad enough to find that due to His protection the Jews had fire from which he could borrow for his own home and share freely with other Christians.