God is the Supreme Being or Creator of the world, according to some religions in the World of Darkness.
Generally, mortals identify God with the monotheistic deity presented by some religions. According to the Abrahamic religions, this god is named as Yahweh, Elohim, Jehovah or Allah. In China, he is known as the August Personage of Jade. That being said, he has many identities and purposes that span across the world.
God was the first being to exist. According to this belief God had no creator and was never made; he has always existed and was present at the beginning of the universe, known to the mages as the Prime. He became lonely and decided to begin Creation.
Vampire: The Masquerade
Vampire: The Masquerade opens up with Caine cursed by God for murdering his brother Abel. Cainite mythology holds up to a high degree, with the story of Caine and Abel recognized by vampires that predate Judaism, and in certain cases recorded by Vampires at some time before Judaism. Special mention of this is made in Demon: The Fallen, where the stories of a certain desert tribe turn out to be unusually accurate - if, from Lucifer's point of view, biased. Obviously, Demons believe in God as much as they believe in themselves. Demons knew God, but their interpretation of God is tied up in a complex love/hate relationship represented by, their Torment. Whatever Demons knew of God, however, they don't know what God is doing right now.
The Kuei-jin believe they know the answer to that one, however. According to the Wan Kuei, the "August Personage of Jade" turned His face on them when he cursed them, much like he did to the Yama Kings when he cursed them. The Wan Kuei believe in a god, they just don't necessarily believe that he's a forgiving god. They know this because they returned from their afterlife in the Yomi Hells.
Hunter: The Reckoning
Which leads us to the Hunters. Imbued by agencies called the Messengers, Hunters may believe they're on a mission from God. The answer is a bit more complex: according to Hunter: The Reckoning, God has largely left the fallen world. Whether permanently or impermanently is open for debate, but the Messengers are God's assistants and are trying desperately to patch up the world before the damage is too severe.
Werewolf: The Apocalypse
Garou and Mages, ironically, have the easiest explanations. The Garou are used to trafficking with spirits, and if someone wishes to address an unusually powerful Celestine as "God", then so be it. The theurges ("god-workers") among the Garou teach a theology which focuses on the Triat and Gaia as the major deities though, so even if a Garou concedes that the god of the Abrahamic religions is a real Celestine they still would not consider him to be a major player in the theomachy in which the multiverse is embroiled. On the other hand, the Bastet creation-myth does include Ahu, the creator of the Triat who in turn created Gaia.
Mage: the Ascension
Of course, the Mage's interpretations of God vary as much as Mage's interpretations of everything else. Certain Traditions (notably the Celestial Chorus) grow in power and enlightenment through a greater understanding of the nature of God, while others such as the Order of Hermes would see Ascension as an apotheosis with Godhead, an act of becoming Godlike, or even unifying with God himself. Others might nominally declare belief in the existence of one or more gods, but deep down see such gods' existences as secondary or even unrelated to their path towards enlightenment (i.e. some members of The Technocracy). Some believe in a pantheon of gods in which the Abrahamic god is not even relevant; examples are theist factions among the Chakravanti and Sahajiya mages who believe in the Hindu trinity of Brahma, Vishnu and Shiva, which some correspond to the Triat (Wyld, Weaver, and Wyrm).
An interesting but not widely discussed interpretation among certain Gnostic Mages stems from the belief that the Awakened Avatar of the Mage is a Godspark or a fragment of God, and that through the Mass Ascension, a shattered God is reunified as those Godsparks within all humanity are able to transcend itself. Some among such mages even classify the various types of Godsparks. Similar notions of a fragmented god can be found among the Kashmiri Shaivite faction of the Chakravanti mages of India. When dealing with Mages as a whole though, anything is open to debate and potentially true.
Wraith: the Oblivion
Ironically, the ones the living consider the closest to God, the wraiths, vary in their viewpoint almost as much as the living. Heretics tend towards Transcendence as the final answer, though whether this is actually related to a god is subject to the individual Heretic. Many more wraiths find their spirituality crushed by the Shadowlands; this is not the heaven or hell they were told of in life, and as a result, they abandon their faith to search for answers on their own. But there are also the Ferrymen who might or might not take worthy souls through the Tempest to the Far Shores which are rumored to reflect individual myths of an afterlife, like Heaven, Hell or Nirvana. Nobody except the Ferrymen ever return, and they refuse to tell.
The answers never come easily; even after the Sixth Great Maelstrom, many of the ghosts of Orpheus maintain belief in a higher power. For some though, it is not the Abrahamic god but rather the dark god called Grandmother.
Demon: the Fallen
The Fallen vary in their attitudes towards God. Like the Yama Kings, they knew Him personally and therefore have a superior understanding of Him compared to other races. After they were cast into the Abyss, they resented Him.
Upon their release by the Sixth Great Maelstrom, they divided themselves into Factions based on their attitudes towards God and humanity: The Reconcilers are penitents who wish to be forgiven and rejoin God; the Raveners are indifferent to Him and wish for Him to unmake them to end their suffering; the Cryptics are curious about God and wish to discover His secrets; the Faustians and Luciferans continue to resent Him and seek to use humanity's Faith as a weapon against Him.